rtfm / SQL / dbishell / src/DBIShell/help/mysql.pm
package DBIShell::help::mysql; use strict; use Exporter (); use vars qw($VERSION @EXPORT @EXPORT_OK %EXPORT_TAGS @ISA %HELP); @ISA = qw(Exporter); @EXPORT = (); @EXPORT_OK = (); %EXPORT_TAGS = (); $VERSION = 0.01_02; use constant H_ARITHMETIC => <<'__arithmetic__'; Arithmetic: The usual arithmetic operators are available. Note that in the case of `-', `+' and `*', the result is calculated with `BIGINT' (64-bit) precision if both arguments are integers! `+' Addition mysql> select 3+5; -> 8 `-' Subtraction mysql> select 3-5; -> -2 `*' Multiplication mysql> select 3*5; -> 15 mysql> select 18014398509481984*18014398509481984.0; -> 324518553658426726783156020576256.0 mysql> select 18014398509481984*18014398509481984; -> 0 The result of the last expression is incorrect because the result of the integer multiplication exceeds the 64-bit range of `BIGINT' calculations. `/' Division mysql> select 3/5; -> 0.60 Division by zero produces a `NULL' result: mysql> select 102/(1-1); -> NULL A division will be calculated with `BIGINT' arithmetic only if performed in a context where its result is converted to an integer! `%' Modulo (like the `%' operator in C). Returns the remainder of `N' divided by `M'. mysql> select MOD(234, 10); -> 4 mysql> select 253 % 7; -> 1 mysql> select MOD(29,9); -> 2 This function is safe to use with `BIGINT' values. __arithmetic__ use constant H_BIT_OPERATORS => <<'__bit_operators__'; Bit Operators: *MySQL* uses `BIGINT' (64-bit) arithmetic for bit operations, so these operators have a maximum range of 64 bits. `|' Bitwise OR mysql> select 29 | 15; -> 31 `&' Bitwise AND mysql> select 29 & 15; -> 13 `<<' Shifts a longlong (`BIGINT') number to the left. mysql> select 1 << 2 -> 4 `>>' Shifts a longlong (`BIGINT') number to the right. mysql> select 4 >> 2 -> 1 `~' Invert all bits. mysql> select 5 & ~1 -> 4 `BIT_COUNT(N)' Returns the number of bits that are set in the argument `N'. mysql> select BIT_COUNT(29); -> 4 __bit_operators__ use constant H_LOGICAL_OPERATORS => <<'__logical_operators__'; Logical Operators: All logical functions return `1' (TRUE) or `0' (FALSE). `NOT' `!' Logical NOT. Returns `1' if the argument is `0', otherwise returns `0'. Exception: `NOT NULL' returns `NULL'. mysql> select NOT 1; -> 0 mysql> select NOT NULL; -> NULL mysql> select ! (1+1); -> 0 mysql> select ! 1+1; -> 1 The last example returns `1' because the expression evaluates the same way as `(!1)+1'. `OR' `||' Logical OR. Returns `1' if either argument is not `0' and not `NULL'. mysql> select 1 || 0; -> 1 mysql> select 0 || 0; -> 0 mysql> select 1 || NULL; -> 1 `AND' `&&' Logical AND. Returns `0' if either argument is `0' or `NULL', otherwise returns `1'. mysql> select 1 && NULL; -> 0 mysql> select 1 && 0; -> 0 __logical_operators__ use constant H_COMPARISON => <<'__comparison__'; Comparison Operators: Comparison operations result in a value of `1' (TRUE), `0' (FALSE) or `NULL'. These functions work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as needed (as in Perl). *MySQL* performs comparisons using the following rules: * If one or both arguments are `NULL', the result of the comparison is `NULL', except for the `<=>' operator. * If both arguments in a comparison operation are strings, they are compared as strings. * If both arguments are integers, they are compared as integers. * Hexadecimal values are treated as binary strings if not compared to a number. * If one of the arguments is a `TIMESTAMP' or `DATETIME' column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. * In all other cases, the arguments are compared as floating-point (real) numbers. By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English). The examples below illustrate conversion of strings to numbers for comparison operations: mysql> SELECT 1 > '6x'; -> 0 mysql> SELECT 7 > '6x'; -> 1 mysql> SELECT 0 > 'x6'; -> 0 mysql> SELECT 0 = 'x6'; -> 1 `=' Equal mysql> select 1 = 0; -> 0 mysql> select '0' = 0; -> 1 mysql> select '0.0' = 0; -> 1 mysql> select '0.01' = 0; -> 0 mysql> select '.01' = 0.01; -> 1 `<>' `!=' Not equal mysql> select '.01' <> '0.01'; -> 1 mysql> select .01 <> '0.01'; -> 0 mysql> select 'zapp' <> 'zappp'; -> 1 `<=' Less than or equal mysql> select 0.1 <= 2; -> 1 `<' Less than mysql> select 2 <= 2; -> 1 `>=' Greater than or equal mysql> select 2 >= 2; -> 1 `>' Greater than mysql> select 2 > 2; -> 0 `<=>' Null safe equal mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL; -> 1 1 0 `IS NULL' `IS NOT NULL' Test whether or not a value is or is not `NULL' mysql> select 1 IS NULL, 0 IS NULL, NULL IS NULL: -> 0 0 1 mysql> select 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL; -> 1 1 0 `expr BETWEEN min AND max' If `expr' is greater than or equal to `min' and `expr' is less than or equal to `max', `BETWEEN' returns `1', otherwise it returns `0'. This is equivalent to the expression `(min <= expr AND expr <= max)' if all the arguments are of the same type. The first argument (`expr') determines how the comparison is performed as follows: * If `expr' is a `TIMESTAMP', `DATE' or `DATETIME' column, min and max are formatted to the same format if they are constants. * If `expr' is a case-insensitive string expression, a case-insensitive string comparison is done. * If `expr' is a case-sensitive string expression, a case-sensitive string comparison is done. * If `expr' is an integer expression, an integer comparison is done. * Otherwise, a floating-point (real) comparison is done. mysql> select 1 BETWEEN 2 AND 3; -> 0 mysql> select 'b' BETWEEN 'a' AND 'c'; -> 1 mysql> select 2 BETWEEN 2 AND '3'; -> 1 mysql> select 2 BETWEEN 2 AND 'x-3'; -> 0 `expr IN (value,...)' Returns `1' if `expr' is any of the values in the `IN' list, else returns `0'. If all values are constants, then all values are evaluated according to the type of `expr' and sorted. The search for the item is then done using a binary search. This means `IN' is very quick if the `IN' value list consists entirely of constants. If `expr' is a case-sensitive string expression, the string comparison is performed in case-sensitive fashion. mysql> select 2 IN (0,3,5,'wefwf'); -> 0 mysql> select 'wefwf' IN (0,3,5,'wefwf'); -> 1 `expr NOT IN (value,...)' Same as `NOT (expr IN (value,...))'. see also: string_comparison, isnull, coalesce, interval __comparison__ use constant H_ISNULL => <<'__isnull__'; ISNULL(expr): If `expr' is `NULL', `ISNULL()' returns `1', otherwise it returns `0'. mysql> select ISNULL(1+1); -> 0 mysql> select ISNULL(1/0); -> 1 Note that a comparison of `NULL' values using `=' will always be false! __isnull__ use constant H_COALESCE => <<'__coalesce__'; COALESCE(list): Returns first non-`NULL' element in list. mysql> select COALESCE(NULL,1); -> 1 mysql> select COALESCE(NULL,NULL,NULL); -> NULL __coalesce__ use constant H_INTERVAL => <<'__interval__'; INTERVAL(N,N1,N2,N3,...): Returns `0' if `N' < `N1', `1' if `N' < `N2' and so on. All arguments are treated as integers. It is required that `N1' < `N2' < `N3' < `...' < `Nn' for this function to work correctly. This is because a binary search is used (very fast). mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200); -> 3 mysql> select INTERVAL(10, 1, 10, 100, 1000); -> 2 mysql> select INTERVAL(22, 23, 30, 44, 200); -> 0 __interval__ use constant H_STRING_COMPARISON => <<'__string_comparison__'; Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion. `expr LIKE pat [ESCAPE 'escape-char']' Pattern matching using SQL simple regular expression comparison. Returns `1' (TRUE) or `0' (FALSE). With `LIKE' you can use the following two wildcard characters in the pattern: `%' Matches any number of characters, even zero characters `_' Matches exactly one character mysql> select 'David!' LIKE 'David_'; -> 1 mysql> select 'David!' LIKE '%D%v%'; -> 1 To test for literal instances of a wildcard character, precede the character with the escape character. If you don't specify the `ESCAPE' character, `\' is assumed: `\%' Matches one `%' character `\_' Matches one `_' character mysql> select 'David!' LIKE 'David\_'; -> 0 mysql> select 'David_' LIKE 'David\_'; -> 1 To specify a different escape character, use the `ESCAPE' clause: mysql> select 'David_' LIKE 'David|_' ESCAPE '|'; -> 1 `LIKE' is allowed on numeric expressions! (This is a *MySQL* extension to the ANSI SQL `LIKE'.) mysql> select 10 LIKE '1%'; -> 1 Note: Because *MySQL* uses the C escape syntax in strings (e.g., `\n'), you must double any `\' that you use in your `LIKE' strings. For example, to search for `\n', specify it as `\\n'. To search for `\', specify it as `\\\\' (the backslashes are stripped once by the parser, and another time when the pattern match is done, leaving a single backslash to be matched). `expr NOT LIKE pat [ESCAPE 'escape-char']' Same as `NOT (expr LIKE pat [ESCAPE 'escape-char'])'. `expr REGEXP pat' `expr RLIKE pat' Performs a pattern match of a string expression `expr' against a pattern `pat'. The pattern can be an extended regular expression. *Note Regexp::. Returns `1' if `expr' matches `pat', otherwise returns `0'. `RLIKE' is a synonym for `REGEXP', provided for `mSQL' compatibility. Note: Because *MySQL* uses the C escape syntax in strings (e.g., `\n'), you must double any `\' that you use in your `REGEXP' strings. In `MySQL' 3.23.4 `REGEXP' is case insensitive for normal (not binary) strings. mysql> select 'Monty!' REGEXP 'm%y%%'; -> 0 mysql> select 'Monty!' REGEXP '.*'; -> 1 mysql> select 'new*\n*line' REGEXP 'new\\*.\\*line'; -> 1 mysql> select "a" REGEXP "A", "a" REGEXP BINARY "A"; -> 1 0 `' `REGEXP' and `RLIKE' use the current character set (ISO-8859-1 Latin1 by default) when deciding the type of a character. `expr NOT REGEXP pat' `expr NOT RLIKE pat' Same as `NOT (expr REGEXP pat)'. see also: comparison, strcmp __string_comparison__ use constant H_STRCMP => <<'__strcmp__'; STRCMP(expr1,expr2): `STRCMP()' returns `0' if the strings are the same, `-1' if the first argument is smaller than the second according to the current sort order, and `1' otherwise. mysql> select STRCMP('text', 'text2'); -> -1 mysql> select STRCMP('text2', 'text'); -> 1 mysql> select STRCMP('text', 'text'); -> 0 __strcmp__ use constant H_BINARY => <<'__binary__'; BINARY: The `BINARY' operator casts the string following it to a binary string. This is an easy way to force a column comparison to be case sensitive even if the column isn't defined as `BINARY' or `BLOB'. mysql> select "a" = "A"; -> 1 mysql> select BINARY "a" = "A"; -> 0 `BINARY' was introduced in *MySQL* 3.23.0 __binary__ use constant H_IFNULL => <<'__ifnull__'; IFNULL(expr1,expr2): If `expr1' is not `NULL', `IFNULL()' returns `expr1', else it returns `expr2'. `IFNULL()' returns a numeric or string value, depending on the context in which it is used. mysql> select IFNULL(1,0); -> 1 mysql> select IFNULL(NULL,10); -> 10 mysql> select IFNULL(1/0,10); -> 10 mysql> select IFNULL(1/0,'yes'); -> 'yes' __ifnull__ use constant H_NULLIF => <<'__nullif__'; NULLIF(expr1,expr2): If `expr1 = expr2' is true, return `NULL' else return `expr1'. This is the same as `CASE WHEN x = y THEN NULL ELSE x END' mysql> select NULLIF(1,1); -> NULL mysql> select NULLIF(1,2); -> 1 Note that `expr1' is evaluated twice in *MySQL* if the arguments are equal. __nullif__ use constant H_IF => <<'__if__'; IF(expr1,expr2,expr3): If `expr1' is TRUE (`expr1 <> 0' and `expr1 <> NULL') then `IF()' returns `expr2', else it returns `expr3'. `IF()' returns a numeric or string value, depending on the context in which it is used. mysql> select IF(1>2,2,3); -> 3 mysql> select IF(1<2,'yes','no'); -> 'yes' mysql> select IF(strcmp('test','test1'),'no','yes'); -> 'no' `expr1' is evaluated as an integer value, which means that if you are testing floating-point or string values, you should do so using a comparison operation. mysql> select IF(0.1,1,0); -> 0 mysql> select IF(0.1<>0,1,0); -> 1 In the first case above, `IF(0.1)' returns `0' because `0.1' is converted to an integer value, resulting in a test of `IF(0)'. This may not be what you expect. In the second case, the comparison tests the original floating-point value to see whether it is non-zero. The result of the comparison is used as an integer. The default return type of `IF()' (which may matter when it stored into a temporary table) is calculated in *MySQL* 3.23 as follows: expr2 or expr3 returns string string expr2 or expr3 returns a floating point value floating point expr2 or expr3 returns an integer integer __if__ use constant H_CASE => <<'__case__'; CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END The first version returns the `result' where `value=compare-value'. The second version returns the result for the first condition which is true. If there was no matching result value, then the result after `ELSE' is returned. If there is no `ELSE' part then `NULL' is returned. mysql> SELECT CASE 1 WHEN 1 THEN "one" WHEN 2 THEN "two" ELSE "more" END; -> "one" mysql> SELECT CASE WHEN 1>0 THEN "true" ELSE "false" END; -> "true" mysql> SELECT CASE BINARY "B" when "a" then 1 when "b" then 2 END; -> NULL __case__ use constant H_FLOW_CONTROL => <<'__flow_control__'; Flow Control: See: ifnull nullif if case __flow_control__ use constant H_ABS => <<'__abs__'; ABS(X): Returns the absolute value of `X'. mysql> select ABS(2); -> 2 mysql> select ABS(-32); -> 32 This function is safe to use with `BIGINT' values. __abs__ use constant H_SIGN => <<'__sign__'; SIGN(X): Returns the sign of the argument as `-1', `0' or `1', depending on whether `X' is negative, zero, or positive. mysql> select SIGN(-32); -> -1 mysql> select SIGN(0); -> 0 mysql> select SIGN(234); -> 1 __sign__ use constant H_MOD => <<'__mod__'; MOD(N,M): Modulo (like the `%' operator in C). Returns the remainder of `N' divided by `M'. mysql> select MOD(234, 10); -> 4 mysql> select 253 % 7; -> 1 mysql> select MOD(29,9); -> 2 This function is safe to use with `BIGINT' values. __mod__ use constant H_FLOOR => <<'__floor__'; FLOOR(X): Returns the largest integer value not greater than `X'. mysql> select FLOOR(1.23); -> 1 mysql> select FLOOR(-1.23); -> -2 Note that the return value is converted to a `BIGINT'! __floor__ use constant H_CEILING => <<'__ceiling__'; CEILING(X): Returns the smallest integer value not less than `X'. mysql> select CEILING(1.23); -> 2 mysql> select CEILING(-1.23); -> -1 Note that the return value is converted to a `BIGINT'! __ceiling__ use constant H_ROUND => <<'__round__'; ROUND(X): Returns the argument `X', rounded to the nearest integer. mysql> select ROUND(-1.23); -> -1 mysql> select ROUND(-1.58); -> -2 mysql> select ROUND(1.58); -> 2 ROUND(X,D): Returns the argument `X', rounded to a number with `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select ROUND(1.298, 1); -> 1.3 mysql> select ROUND(1.298, 0); -> 1 __round__ use constant H_EXP => <<'__exp__'; EXP(X): Returns the value of `e' (the base of natural logarithms) raised to the power of `X'. mysql> select EXP(2); -> 7.389056 mysql> select EXP(-2); -> 0.135335 __exp__ use constant H_LOG => <<'__log__'; LOG(X): Returns the natural logarithm of `X'. mysql> select LOG(2); -> 0.693147 mysql> select LOG(-2); -> NULL If you want the log of a number `X' to some arbitary base `B', use the formula `LOGB(X) = LOG(X)/LOG(B)'. __log__ use constant H_LOG10 => <<'__log10__'; LOG10(X): Returns the base-10 logarithm of `X'. mysql> select LOG10(2); -> 0.301030 mysql> select LOG10(100); -> 2.000000 mysql> select LOG10(-100); -> NULL __log10__ use constant H_POW => <<'__pow__'; POW(X,Y): Returns the value of `X' raised to the power of `Y'. mysql> select POW(2,2); -> 4.000000 mysql> select POW(2,-2); -> 0.250000 __pow__ use constant H_POWER => H_POW; use constant H_SQRT => <<'__sqrt__'; SQRT(X): Returns the non-negative square root of `X'. mysql> select SQRT(4); -> 2.000000 mysql> select SQRT(20); -> 4.472136 __sqrt__ use constant H_PI => <<'__pi__'; PI(): Returns the value of PI. mysql> select PI(); -> 3.141593 __pi__ use constant H_COS => <<'__cos__'; COS(X): Returns the cosine of `X', where `X' is given in radians. mysql> select COS(PI()); -> -1.000000 __cos__ use constant H_SIN => <<'__sin__'; SIN(X): Returns the sine of `X', where `X' is given in radians. mysql> select SIN(PI()); -> 0.000000 __sin__ use constant H_TAN => <<'__tan__'; TAN(X): Returns the tangent of `X', where `X' is given in radians. mysql> select TAN(PI()+1); -> 1.557408 __tan__ use constant H_ACOS => <<'__acos__'; ACOS(X): Returns the arc cosine of `X', that is, the value whose cosine is `X'. Returns `NULL' if `X' is not in the range `-1' to `1'. mysql> select ACOS(1); -> 0.000000 mysql> select ACOS(1.0001); -> NULL mysql> select ACOS(0); -> 1.570796 __acos__ use constant H_ASIN => <<'__asin__'; ASIN(X): Returns the arc sine of `X', that is, the value whose sine is `X'. Returns `NULL' if `X' is not in the range `-1' to `1'. mysql> select ASIN(0.2); -> 0.201358 mysql> select ASIN('foo'); -> 0.000000 __asin__ use constant H_ATAN => <<'__atan__'; ATAN(X): Returns the arc tangent of `X', that is, the value whose tangent is `X'. mysql> select ATAN(2); -> 1.107149 mysql> select ATAN(-2); -> -1.107149 __atan__ use constant H_ATAN2 => <<'__atan2__'; ATAN2(X,Y): Returns the arc tangent of the two variables `X' and `Y'. It is similar to calculating the arc tangent of `Y / X', except that the signs of both arguments are used to determine the quadrant of the result. mysql> select ATAN(-2,2); -> -0.785398 mysql> select ATAN(PI(),0); -> 1.570796 __atan2__ use constant H_COT => <<'__cot__'; COT(X): Returns the cotangent of `X'. mysql> select COT(12); -> -1.57267341 mysql> select COT(0); -> NULL __cot__ use constant H_RAND => <<'__rand__'; RAND(N): Returns a random floating-point value in the range `0' to `1.0'. If an integer argument `N' is specified, it is used as the seed value. mysql> select RAND(); -> 0.5925 mysql> select RAND(20); -> 0.1811 mysql> select RAND(20); -> 0.1811 mysql> select RAND(); -> 0.2079 mysql> select RAND(); -> 0.7888 You can't use a column with `RAND()' values in an `ORDER BY' clause, because `ORDER BY' would evaluate the column multiple times. In *MySQL* 3.23, you can however do: `SELECT * FROM table_name ORDER BY RAND()' This is useful to get a random sample of a set `SELECT * FROM table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000'. Note that a `RAND()' in a `WHERE' clause will be re-evaluated every time the `WHERE' is executed. __rand__ use constant H_LEAST => <<'__least__'; LEAST(X,Y,...): With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules: * If the return value is used in an `INTEGER' context, or all arguments are integer-valued, they are compared as integers. * If the return value is used in a `REAL' context, or all arguments are real-valued, they are compared as reals. * If any argument is a case-sensitive string, the arguments are compared as case-sensitive strings. * In other cases, the arguments are compared as case-insensitive strings. mysql> select LEAST(2,0); -> 0 mysql> select LEAST(34.0,3.0,5.0,767.0); -> 3.0 mysql> select LEAST("B","A","C"); -> "A" In *MySQL* versions prior to 3.22.5, you can use `MIN()' instead of `LEAST'. __least__ use constant H_GREATEST => <<'__greatest__'; GREATEST(X,Y,...): Returns the largest (maximum-valued) argument. The arguments are compared using the same rules as for `LEAST'. mysql> select GREATEST(2,0); -> 2 mysql> select GREATEST(34.0,3.0,5.0,767.0); -> 767.0 mysql> select GREATEST("B","A","C"); -> "C" In *MySQL* versions prior to 3.22.5, you can use `MAX()' instead of `GREATEST'. __greatest__ use constant H_DEGREES => <<'__degrees__'; DEGREES(X): Returns the argument `X', converted from radians to degrees. mysql> select DEGREES(PI()); -> 180.000000 __degrees__ use constant H_RADIANS => <<'__radians__'; RADIANS(X): Returns the argument `X', converted from degrees to radians. mysql> select RADIANS(90); -> 1.570796 __radians__ use constant H_TRUNCATE => <<'__truncate__'; TRUNCATE(X,D): Returns the number `X', truncated to `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select TRUNCATE(1.223,1); -> 1.2 mysql> select TRUNCATE(1.999,1); -> 1.9 mysql> select TRUNCATE(1.999,0); -> 1 __truncate__ use constant H_NUMERIC_FUNCTIONS => <<'__numeric_functions__'; Numeric Functions: abs sign mod floor ceiling round round exp log log10 pow sqrt pi cos sin tan acos asin atan atan2 cot rand least greatest degrees radians truncate __numeric_functions__ use constant H_ASCII => <<'__ascii__'; ASCII(str): Returns the ASCII code value of the leftmost character of the string `str'. Returns `0' if `str' is the empty string. Returns `NULL' if `str' is `NULL'. mysql> select ASCII('2'); -> 50 mysql> select ASCII(2); -> 50 mysql> select ASCII('dx'); -> 100 See also the `ORD()' function. __ascii__ use constant H_ORD => <<'__ord__'; ORD(str): If the leftmost character of the string str is a multi-byte character, returns the code of multi-byte character by returning the ASCII code value of the character in the format of: `((first byte ASCII code)*256+(second byte ASCII code))[*256+third byte ASCII code...]'. If the leftmost character is not a multi-byte character, returns the same value as the like `ASCII()' function does. mysql> select ORD('2'); -> 50 __ord__ use constant H_CONV => <<'__conv__'; CONV(N,from_base,to_base): Converts numbers between different number bases. Returns a string representation of the number `N', converted from base `from_base' to base `to_base'. Returns `NULL' if any argument is `NULL'. The argument `N' is interpreted as an integer, but may be specified as an integer or a string. The minimum base is `2' and the maximum base is `36'. If `to_base' is a negative number, `N' is regarded as a signed number. Otherwise, `N' is treated as unsigned. `CONV' works with 64-bit precision. mysql> select CONV("a",16,2); -> '1010' mysql> select CONV("6E",18,8); -> '172' mysql> select CONV(-17,10,-18); -> '-H' mysql> select CONV(10+"10"+'10'+0xa,10,10); -> '40' __conv__ use constant H_BIN => <<'__bin__'; BIN(N): Returns a string representation of the binary value of `N', where `N' is a longlong (`BIGINT') number. This is equivalent to `CONV(N,10,2)'. Returns `NULL' if `N' is `NULL'. mysql> select BIN(12); -> '1100' __bin__ use constant H_OCT => <<'__oct__'; OCT(N): Returns a string representation of the octal value of `N', where `N' is a longlong number. This is equivalent to `CONV(N,10,8)'. Returns `NULL' if `N' is `NULL'. mysql> select OCT(12); -> '14' __oct__ use constant H_HEX => <<'__hex__'; HEX(N): Returns a string representation of the hexadecimal value of `N', where `N' is a longlong (`BIGINT') number. This is equivalent to `CONV(N,10,16)'. Returns `NULL' if `N' is `NULL'. mysql> select HEX(255); -> 'FF' __hex__ use constant H_CHAR => <<'__char__'; CHAR(N,...): `CHAR()' interprets the arguments as integers and returns a string consisting of the characters given by the ASCII code values of those integers. `NULL' values are skipped. mysql> select CHAR(77,121,83,81,'76'); -> 'MySQL' mysql> select CHAR(77,77.3,'77.3'); -> 'MMM' __char__ use constant H_CONCAT => <<'__concat__'; CONCAT(str1,str2,...): Returns the string that results from concatenating the arguments. Returns `NULL' if any argument is `NULL'. May have more than 2 arguments. A numeric argument is converted to the equivalent string form. mysql> select CONCAT('My', 'S', 'QL'); -> 'MySQL' mysql> select CONCAT('My', NULL, 'QL'); -> NULL mysql> select CONCAT(14.3); -> '14.3' __concat__ use constant H_CONCAT_WS => <<'__concat_ws__'; CONCAT_WS(separator, str1, str2,...): `CONCAT_WS()' stands for CONCAT With Separator and is a special form of `CONCAT()'. The irst argument is the separator for the rest of the arguments. The separator can be a string as well as the rest of the arguments. If the separator is `NULL', the result will be `NULL'. The function will skip any `NULL's and empty strings, after the separator argument. The separator will be added between the strings to be concatenated. mysql> select CONCAT_WS(",","First name","Second name","Last Name"); -> 'First name,Second name,Last Name' mysql> select CONCAT_WS(",","First name",NULL,"Last Name"); -> 'First name,Last Name' __concat_ws__ use constant H_LENGTH => <<'__length__'; LENGTH(str): __length__ use constant H_OCTET_LENGTH => <<'__octet_length__'; OCTET_LENGTH(str): __octet_length__ use constant H_CHAR_LENGTH => <<'__char_length__'; CHAR_LENGTH(str): __char_length__ use constant H_CHARACTER_LENGTH => <<'__character_length__'; CHARACTER_LENGTH(str): Returns the length of the string `str'. mysql> select LENGTH('text'); -> 4 mysql> select OCTET_LENGTH('text'); -> 4 Note that for `CHAR_LENGTH()', multi-byte characters are only counted once. __character_length__ use constant H_POSITION => <<'__position__'; POSITION(substr IN str): Returns the position of the first occurrence of substring `substr' in string `str'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar'); -> 4 mysql> select LOCATE('xbar', 'foobar'); -> 0 This function is multi-byte safe. __position__ use constant H_LOCATE => <<'__locate__'; LOCATE(substr,str): LOCATE(substr,str,pos): Returns the position of the first occurrence of substring `substr' in string `str', starting at position `pos'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar',5); -> 7 This function is multi-byte safe. __locate__ use constant H_INSTR => <<'__instr__'; INSTR(str,substr): Returns the position of the first occurrence of substring `substr' in string `str'. This is the same as the two-argument form of `LOCATE()', except that the arguments are swapped. mysql> select INSTR('foobarbar', 'bar'); -> 4 mysql> select INSTR('xbar', 'foobar'); -> 0 This function is multi-byte safe. __instr__ use constant H_LPAD => <<'__lpad__'; LPAD(str,len,padstr): Returns the string `str', left-padded with the string `padstr' until `str' is `len' characters long. mysql> select LPAD('hi',4,'??'); -> '??hi' __lpad__ use constant H_RPAD => <<'__rpad__'; RPAD(str,len,padstr): Returns the string `str', right-padded with the string `padstr' until `str' is `len' characters long. mysql> select RPAD('hi',5,'?'); -> 'hi???' __rpad__ use constant H_LEFT => <<'__left__'; LEFT(str,len): Returns the leftmost `len' characters from the string `str'. mysql> select LEFT('foobarbar', 5); -> 'fooba' This function is multi-byte safe. __left__ use constant H_RIGHT => <<'__right__'; RIGHT(str,len): Returns the rightmost `len' characters from the string `str'. mysql> select RIGHT('foobarbar', 4); -> 'rbar' This function is multi-byte safe. __right__ use constant H_MID => <<'__mid__'; MID(str,pos,len): Returns a substring `len' characters long from string `str', starting at position `pos'. The variant form that uses `FROM' is ANSI SQL92 syntax. mysql> select SUBSTRING('Quadratically',5,6); -> 'ratica' This function is multi-byte safe. __mid__ use constant H_SUBSTRING => <<'__substring__'; SUBSTRING(str,pos,len): SUBSTRING(str FROM pos FOR len): SUBSTRING(str,pos): SUBSTRING(str FROM pos): Returns a substring from string `str' starting at position `pos'. mysql> select SUBSTRING('Quadratically',5); -> 'ratically' mysql> select SUBSTRING('foobarbar' FROM 4); -> 'barbar' This function is multi-byte safe. __substring__ use constant H_SUBSTRING_INDEX => <<'__substring_index__'; SUBSTRING_INDEX(str,delim,count): Returns the substring from string `str' before `count' occurrences of the delimiter `delim'. If `count' is positive, everything to the left of the final delimiter (counting from the left) is returned. If `count' is negative, everything to the right of the final delimiter (counting from the right) is returned. mysql> select SUBSTRING_INDEX('www.mysql.com', '.', 2); -> 'www.mysql' mysql> select SUBSTRING_INDEX('www.mysql.com', '.', -2); -> 'mysql.com' This function is multi-byte safe. __substring_index__ use constant H_LTRIM => <<'__ltrim__'; LTRIM(str): Returns the string `str' with leading space characters removed. mysql> select LTRIM(' barbar'); -> 'barbar' __ltrim__ use constant H_RTRIM => <<'__rtrim__'; RTRIM(str): Returns the string `str' with trailing space characters removed. mysql> select RTRIM('barbar '); -> 'barbar' This function is multi-byte safe. __rtrim__ use constant H_TRIM => <<'__trim__'; TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str): Returns the string `str' with all `remstr' prefixes and/or suffixes removed. If none of the specifiers `BOTH', `LEADING' or `TRAILING' are given, `BOTH' is assumed. If `remstr' is not specified, spaces are removed. mysql> select TRIM(' bar '); -> 'bar' mysql> select TRIM(LEADING 'x' FROM 'xxxbarxxx'); -> 'barxxx' mysql> select TRIM(BOTH 'x' FROM 'xxxbarxxx'); -> 'bar' mysql> select TRIM(TRAILING 'xyz' FROM 'barxxyz'); -> 'barx' This function is multi-byte safe. __trim__ use constant H_SOUNDEX => <<'__soundex__'; SOUNDEX(str): Returns a soundex string from `str'. Two strings that sound "about the same" should have identical soundex strings. A "standard" soundex string is 4 characters long, but the `SOUNDEX()' function returns an arbitrarily long string. You can use `SUBSTRING()' on the result to get a "standard" soundex string. All non-alphanumeric characters are ignored in the given string. All international alpha characters outside the A-Z range are treated as vowels. mysql> select SOUNDEX('Hello'); -> 'H400' mysql> select SOUNDEX('Quadratically'); -> 'Q36324' __soundex__ use constant H_SPACE => <<'__space__'; SPACE(N): Returns a string consisting of `N' space characters. mysql> select SPACE(6); -> ' ' __space__ use constant H_FN_REPLACE => <<'__replace__'; REPLACE(str,from_str,to_str): Returns the string `str' with all all occurrences of the string `from_str' replaced by the string `to_str'. mysql> select REPLACE('www.mysql.com', 'w', 'Ww'); -> 'WwWwWw.mysql.com' This function is multi-byte safe. __replace__ use constant H_REPEAT => <<'__repeat__'; REPEAT(str,count): Returns a string consisting of the string `str' repeated `count' times. If `count <= 0', returns an empty string. Returns `NULL' if `str' or `count' are `NULL'. mysql> select REPEAT('MySQL', 3); -> 'MySQLMySQLMySQL' __repeat__ use constant H_REVERSE => <<'__reverse__'; REVERSE(str): Returns the string `str' with the order of the characters reversed. mysql> select REVERSE('abc'); -> 'cba' This function is multi-byte safe. __reverse__ use constant H_FN_INSERT => <<'__insert__'; INSERT(str,pos,len,newstr): Returns the string `str', with the substring beginning at position `pos' and `len' characters long replaced by the string `newstr'. mysql> select INSERT('Quadratic', 3, 4, 'What'); -> 'QuWhattic' This function is multi-byte safe. __insert__ use constant H_ELT => <<'__elt__'; ELT(N,str1,str2,str3,...): Returns `str1' if `N' = `1', `str2' if `N' = `2', and so on. Returns `NULL' if `N' is less than `1' or greater than the number of arguments. `ELT()' is the complement of `FIELD()'. mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo'); -> 'ej' mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo'); -> 'foo' __elt__ use constant H_FIELD => <<'__field__'; FIELD(str,str1,str2,str3,...): Returns the index of `str' in the `str1', `str2', `str3', `...' list. Returns `0' if `str' is not found. `FIELD()' is the complement of `ELT()'. mysql> select FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 2 mysql> select FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 0 __field__ use constant H_FIND_IN_SET => <<'__find_in_set__'; FIND_IN_SET(str,strlist): Returns a value `1' to `N' if the string `str' is in the list `strlist' consisting of `N' substrings. A string list is a string composed of substrings separated by `,' characters. If the first argument is a constant string and the second is a column of type `SET', the `FIND_IN_SET()' function is optimized to use bit arithmetic! Returns `0' if `str' is not in `strlist' or if `strlist' is the empty string. Returns `NULL' if either argument is `NULL'. This function will not work properly if the first argument contains a `,'. mysql> SELECT FIND_IN_SET('b','a,b,c,d'); -> 2 __find_in_set__ use constant H_MAKE_SET => <<'__make_set__'; MAKE_SET(bits,str1,str2,...): Returns a set (a string containing substrings separated by `,' characters) consisting of the strings that have the corresponding bit in `bits' set. `str1' corresponds to bit 0, `str2' to bit 1, etc. `NULL' strings in `str1', `str2', `...' are not appended to the result. mysql> SELECT MAKE_SET(1,'a','b','c'); -> 'a' mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world'); -> 'hello,world' mysql> SELECT MAKE_SET(0,'a','b','c'); -> '' __make_set__ use constant H_EXPORT_SET => <<'__export_set__'; EXPORT_SET(bits,on,off,[separator,[number_of_bits]]): Returns a string where for every bit set in 'bit', you get a 'on' string and for every reset bit you get an 'off' string. Each string is separated with 'separator' (default ',') and only 'number_of_bits' (default 64) of 'bits' is used. mysql> select EXPORT_SET(5,'Y','N',',',4) -> Y,N,Y,N __export_set__ use constant H_LCASE => <<'__lcase__'; LCASE(str): __lcase__ use constant H_LOWER => <<'__lower__'; LOWER(str): Returns the string `str' with all characters changed to lowercase according to the current character set mapping (the default is ISO-8859-1 Latin1). This function is multi-byte safe. mysql> select LCASE('QUADRATICALLY'); -> 'quadratically' __lower__ use constant H_UCASE => <<'__ucase__'; UCASE(str): __ucase__ use constant H_UPPER => <<'__upper__'; UPPER(str): Returns the string `str' with all characters changed to uppercase according to the current character set mapping (the default is ISO-8859-1 Latin1). mysql> select UCASE('Hej'); -> 'HEJ' This function is multi-byte safe. __upper__ use constant H_LOAD_FILE => <<'__load_file__'; LOAD_FILE(file_name): Reads the file and returns the file contents as a string. The file must be on the server, you must specify the full pathname to the file, and you must have the *file* privilege. The file must be readable by all and be smaller than `max_allowed_packet'. If the file doesn't exist or can't be read due to one of the above reasons, the function returns `NULL'. mysql> UPDATE table_name SET blob_column=LOAD_FILE("/tmp/picture") WHERE id=1; If you are not using *MySQL 3.23*, you have to do the reading of the file inside your application and create an `INSERT' statement to update the database with the file information. One way to do this, if you are using the *MySQL*++ library, can be found at `http://www.mysql.com/documentation/mysql++/mysql++-examples.html'. *MySQL* automatically converts numbers to strings as necessary, and vice versa: mysql> SELECT 1+"1"; -> 2 mysql> SELECT CONCAT(2,' test'); -> '2 test' If you want to convert a number to a string explicitly, pass it as the argument to `CONCAT()'. If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons. __load_file__ use constant H_STRING_FUNCTIONS => <<'__string_functions__'; String Functions: String-valued functions return `NULL' if the length of the result would be greater than the `max_allowed_packet' server parameter. For functions that operate on string positions, the first position is numbered 1. ascii ord conv bin oct hex char concat concat_ws length octet_length char_length character_length locate position instr lpad rpad left right substring substring mid substring substring_index ltrim rtrim trim soundex space replace [see fn_replace] repeat reverse insert [see fn_insert] elt field find_in_set make_set export_set lcase lower ucase upper load_file __string_functions__ use constant H_DAYOFWEEK => <<'__dayofweek__'; DAYOFWEEK(date): Returns the weekday index for `date' (`1' = Sunday, `2' = Monday, ... `7' = Saturday). These index values correspond to the ODBC standard. mysql> select DAYOFWEEK('1998-02-03'); -> 3 __dayofweek__ use constant H_WEEKDAY => <<'__weekday__'; WEEKDAY(date): Returns the weekday index for `date' (`0' = Monday, `1' = Tuesday, ... `6' = Sunday). mysql> select WEEKDAY('1997-10-04 22:23:00'); -> 5 mysql> select WEEKDAY('1997-11-05'); -> 2 __weekday__ use constant H_DAYOFMONTH => <<'__dayofmonth__'; DAYOFMONTH(date): Returns the day of the month for `date', in the range `1' to `31'. mysql> select DAYOFMONTH('1998-02-03'); -> 3 __dayofmonth__ use constant H_DAYOFYEAR => <<'__dayofyear__'; DAYOFYEAR(date): Returns the day of the year for `date', in the range `1' to `366'. mysql> select DAYOFYEAR('1998-02-03'); -> 34 __dayofyear__ use constant H_MONTH => <<'__month__'; MONTH(date): Returns the month for `date', in the range `1' to `12'. mysql> select MONTH('1998-02-03'); -> 2 __month__ use constant H_DAYNAME => <<'__dayname__'; DAYNAME(date): Returns the name of the weekday for `date'. mysql> select DAYNAME("1998-02-05"); -> 'Thursday' __dayname__ use constant H_MONTHNAME => <<'__monthname__'; MONTHNAME(date): Returns the name of the month for `date'. mysql> select MONTHNAME("1998-02-05"); -> 'February' __monthname__ use constant H_QUARTER => <<'__quarter__'; QUARTER(date): Returns the quarter of the year for `date', in the range `1' to `4'. mysql> select QUARTER('98-04-01'); -> 2 __quarter__ use constant H_WEEK => <<'__week__'; WEEK(date): WEEK(date,first): With a single argument, returns the week for `date', in the range `0' to `53' (yes, there may be the beginnings of a week 53), for locations where Sunday is the first day of the week. The two-argument form of `WEEK()' allows you to specify whether the week starts on Sunday or Monday. The week starts on Sunday if the second argument is `0', on Monday if the second argument is `1'. mysql> select WEEK('1998-02-20'); -> 7 mysql> select WEEK('1998-02-20',0); -> 7 mysql> select WEEK('1998-02-20',1); -> 8 mysql> select WEEK('1998-12-31',1); -> 53 __week__ use constant H_YEAR => <<'__year__'; YEAR(date): Returns the year for `date', in the range `1000' to `9999'. mysql> select YEAR('98-02-03'); -> 1998 __year__ use constant H_YEARWEEK => <<'__yearweek__'; YEARWEEK(date): YEARWEEK(date,first): Returns year and week for a date. The second arguments works exactly like the second argument to `WEEK()'. Note that the year may be different from the year in the date argument for the first and the last week of the year! mysql> select YEARWEEK('1987-01-01'); -> 198653 __yearweek__ use constant H_HOUR => <<'__hour__'; HOUR(time): Returns the hour for `time', in the range `0' to `23'. mysql> select HOUR('10:05:03'); -> 10 __hour__ use constant H_MINUTE => <<'__minute__'; MINUTE(time): Returns the minute for `time', in the range `0' to `59'. mysql> select MINUTE('98-02-03 10:05:03'); -> 5 __minute__ use constant H_SECOND => <<'__second__'; SECOND(time): Returns the second for `time', in the range `0' to `59'. mysql> select SECOND('10:05:03'); -> 3 __second__ use constant H_PERIOD_ADD => <<'__period_add__'; PERIOD_ADD(P,N): Adds `N' months to period `P' (in the format `YYMM' or `YYYYMM'). Returns a value in the format `YYYYMM'. Note that the period argument `P' is _not_ a date value. mysql> select PERIOD_ADD(9801,2); -> 199803 __period_add__ use constant H_PERIOD_DIFF => <<'__period_diff__'; PERIOD_DIFF(P1,P2): Returns the number of months between periods `P1' and `P2'. `P1' and `P2' should be in the format `YYMM' or `YYYYMM'. Note that the period arguments `P1' and `P2' are _not_ date values. mysql> select PERIOD_DIFF(9802,199703); -> 11 __period_diff__ use constant H_DATE_ADD => <<'__date_add__'; DATE_ADD(date,INTERVAL expr type): DATE_SUB(date,INTERVAL expr type): ADDDATE(date,INTERVAL expr type): SUBDATE(date,INTERVAL expr type): These functions perform date arithmetic. They are new for *MySQL* 3.22. `ADDDATE()' and `SUBDATE()' are synonyms for `DATE_ADD()' and `DATE_SUB()'. In *MySQL* 3.23, you can use `+' and `-' instead of `DATE_ADD()' and `DATE_SUB()'. (See example) `date' is a `DATETIME' or `DATE' value specifying the starting date. `expr' is an expression specifying the interval value to be added or substracted from the starting date. `expr' is a string; it may start with a `-' for negative intervals. `type' is a keyword indicating how the expression should be interpreted. The `EXTRACT(type FROM date)' function returns the 'type' interval from the date. The following table shows how the `type' and `expr' arguments are related: `type' *Meaning* *Expected* `expr' *format* *value* `SECOND' Seconds `SECONDS' `MINUTE' Minutes `MINUTES' `HOUR' Hours `HOURS' `DAY' Days `DAYS' `MONTH' Months `MONTHS' `YEAR' Years `YEARS' `MINUTE_SECOND'Minutes and seconds `"MINUTES:SECONDS"' `HOUR_MINUTE'Hours and minutes `"HOURS:MINUTES"' `DAY_HOUR' Days and hours `"DAYS HOURS"' `YEAR_MONTH' Years and months `"YEARS-MONTHS"' `HOUR_SECOND'Hours, minutes, `"HOURS:MINUTES:SECONDS"' `DAY_MINUTE' Days, hours, `"DAYS HOURS:MINUTES"' minutes `DAY_SECOND' Days, hours, `"DAYS minutes, seconds HOURS:MINUTES:SECONDS"' *MySQL* allows any punctuation delimiter in the `expr' format. The ones shown in the table are the suggested delimiters. If the `date' argument is a `DATE' value and your calculations involve only `YEAR', `MONTH' and `DAY' parts (that is, no time parts), the result is a `DATE' value. Otherwise the result is a `DATETIME' value. mysql> SELECT "1997-12-31 23:59:59" + INTERVAL 1 SECOND; -> 1998-01-01 00:00:00 mysql> SELECT INTERVAL 1 DAY + "1997-12-31"; -> 1998-01-01 mysql> SELECT "1998-01-01" - INTERVAL 1 SECOND; -> 1997-12-31 23:59:59 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL 1 SECOND); -> 1998-01-01 00:00:00 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL 1 DAY); -> 1998-01-01 23:59:59 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL "1:1" MINUTE_SECOND); -> 1998-01-01 00:01:00 mysql> SELECT DATE_SUB("1998-01-01 00:00:00", INTERVAL "1 1:1:1" DAY_SECOND); -> 1997-12-30 22:58:59 mysql> SELECT DATE_ADD("1998-01-01 00:00:00", INTERVAL "-1 10" DAY_HOUR); -> 1997-12-30 14:00:00 mysql> SELECT DATE_SUB("1998-01-02", INTERVAL 31 DAY); -> 1997-12-02 mysql> SELECT EXTRACT(YEAR FROM "1999-07-02"); -> 1999 mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03"); -> 199907 mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03"); -> 20102 If you specify an interval value that is too short (does not include all the interval parts that would be expected from the `type' keyword), *MySQL* assumes you have left out the leftmost parts of the interval value. For example, if you specify a `type' of `DAY_SECOND', the value of `expr' is expected to have days, hours, minutes and seconds parts. If you specify a value like `"1:10"', *MySQL* assumes that the days and hours parts are missing and the value represents minutes and seconds. In other words, `"1:10" DAY_SECOND' is interpreted in such a way that it is equivalent to `"1:10" MINUTE_SECOND'. This is analogous to the way that *MySQL* interprets `TIME' values as representing elapsed time rather than as time of day. If you use really incorrect dates, the result is `NULL'. If you add `MONTH', `YEAR_MONTH' or `YEAR' and the resulting date has a day that is larger than the maximum day for the new month, the day is adjusted to the maximum days in the new month. mysql> select DATE_ADD('1998-01-30', Interval 1 month); -> 1998-02-28 Note from the preceding example that the word `INTERVAL' and the `type' keyword are not case sensitive. __date_add__ use constant H_DATE_SUB => H_DATE_ADD; use constant H_ADDDATE => H_DATE_ADD; use constant H_SUBDATE => H_DATE_ADD; use constant H_TO_DAYS => <<'__to_days__'; TO_DAYS(date): Given a date `date', returns a daynumber (the number of days since year 0). mysql> select TO_DAYS(950501); -> 728779 mysql> select TO_DAYS('1997-10-07'); -> 729669 `TO_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it doesn't take into account the days that were lost when the calender was changed. __to_days__ use constant H_FROM_DAYS => <<'__from_days__'; FROM_DAYS(N): Given a daynumber `N', returns a `DATE' value. mysql> select FROM_DAYS(729669); -> '1997-10-07' `FROM_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it doesn't take into account the days that were lost when the calender was changed. __from_days__ use constant H_DATE_FORMAT => <<'__date_format__'; DATE_FORMAT(date,format): Formats the `date' value according to the `format' string. The following specifiers may be used in the `format' string: `%M' Month name (`January'..`December') `%W' Weekday name (`Sunday'..`Saturday') `%D' Day of the month with english suffix (`1st', `2nd', `3rd', etc.) `%Y' Year, numeric, 4 digits `%y' Year, numeric, 2 digits `%X' Year for the week where Sunday is the first day of the week, numeric, 4 digits, used with '%V' `%x' Year for the week, where Monday is the first day of the week, numeric, 4 digits, used with '%v' `%a' Abbreviated weekday name (`Sun'..`Sat') `%d' Day of the month, numeric (`00'..`31') `%e' Day of the month, numeric (`0'..`31') `%m' Month, numeric (`01'..`12') `%c' Month, numeric (`1'..`12') `%b' Abbreviated month name (`Jan'..`Dec') `%j' Day of year (`001'..`366') `%H' Hour (`00'..`23') `%k' Hour (`0'..`23') `%h' Hour (`01'..`12') `%I' Hour (`01'..`12') `%l' Hour (`1'..`12') `%i' Minutes, numeric (`00'..`59') `%r' Time, 12-hour (`hh:mm:ss [AP]M') `%T' Time, 24-hour (`hh:mm:ss') `%S' Seconds (`00'..`59') `%s' Seconds (`00'..`59') `%p' `AM' or `PM' `%w' Day of the week (`0'=Sunday..`6'=Saturday) `%U' Week (`0'..`53'), where Sunday is the first day of the week `%u' Week (`0'..`53'), where Monday is the first day of the week `%V' Week (`1'..`53'), where Sunday is the first day of the week. Used with '%X' `%v' Week (`1'..`53'), where Monday is the first day of the week. Used with '%x' `%%' A literal `%'. All other characters are just copied to the result without interpretation. mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y'); -> 'Saturday October 1997' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s'); -> '22:23:00' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%D %y %a %d %m %b %j'); -> '4th 97 Sat 04 10 Oct 277' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H %k %I %r %T %S %w'); -> '22 22 10 10:23:00 PM 22:23:00 00 6' mysql> select DATE_FORMAT('1999-01-01', '%X %V'); -> '1998 52' As of *MySQL* 3.23, the `%' character is required before format specifier characters. In earlier versions of *MySQL*, `%' was optional. __date_format__ use constant H_TIME_FORMAT => <<'__time_format__'; TIME_FORMAT(time,format): This is used like the `DATE_FORMAT()' function above, but the `format' string may contain only those format specifiers that handle hours, minutes and seconds. Other specifiers produce a `NULL' value or `0'. __time_format__ use constant H_CURDATE => <<'__curdate__'; CURDATE(): CURRENT_DATE: Returns today's date as a value in `'YYYY-MM-DD'' or `YYYYMMDD' format, depending on whether the function is used in a string or numeric context. mysql> select CURDATE(); -> '1997-12-15' mysql> select CURDATE() + 0; -> 19971215 __curdate__ use constant H_CURTIME => <<'__curtime__'; CURTIME(): CURRENT_TIME: Returns the current time as a value in `'HH:MM:SS'' or `HHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select CURTIME(); -> '23:50:26' mysql> select CURTIME() + 0; -> 235026 __curtime__ use constant H_NOW => <<'__now__'; NOW(): SYSDATE(): CURRENT_TIMESTAMP: Returns the current date and time as a value in `'YYYY-MM-DD HH:MM:SS'' or `YYYYMMDDHHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select NOW(); -> '1997-12-15 23:50:26' mysql> select NOW() + 0; -> 19971215235026 __now__ use constant H_SYSDATE => H_NOW; use constant H_UNIX_TIMESTAMP => <<'__unix_timestamp__'; UNIX_TIMESTAMP(): UNIX_TIMESTAMP(date): If called with no argument, returns a Unix timestamp (seconds since `'1970-01-01 00:00:00'' GMT). If `UNIX_TIMESTAMP()' is called with a `date' argument, it returns the value of the argument as seconds since `'1970-01-01 00:00:00'' GMT. `date' may be a `DATE' string, a `DATETIME' string, a `TIMESTAMP', or a number in the format `YYMMDD' or `YYYYMMDD' in local time. mysql> select UNIX_TIMESTAMP(); -> 882226357 mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00'); -> 875996580 When `UNIX_TIMESTAMP' is used on a `TIMESTAMP' column, the function will receive the value directly, with no implicit "string-to-unix-timestamp" conversion. If you give `UNIX_TIMESTAMP()' a wrong or out-of-range date, it will return 0. __unix_timestamp__ use constant H_FROM_UNIXTIME => <<'__from_unixtime__'; FROM_UNIXTIME(unix_timestamp): Returns a representation of the `unix_timestamp' argument as a value in `'YYYY-MM-DD HH:MM:SS'' or `YYYYMMDDHHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select FROM_UNIXTIME(875996580); -> '1997-10-04 22:23:00' mysql> select FROM_UNIXTIME(875996580) + 0; -> 19971004222300 FROM_UNIXTIME(unix_timestamp,format): Returns a string representation of the Unix timestamp, formatted according to the `format' string. `format' may contain the same specifiers as those listed in the entry for the `DATE_FORMAT()' function. mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(), '%Y %D %M %h:%i:%s %x'); -> '1997 23rd December 03:43:30 x' __from_unixtime__ use constant H_SEC_TO_TIME => <<'__sec_to_time__'; SEC_TO_TIME(seconds): Returns the `seconds' argument, converted to hours, minutes and seconds, as a value in `'HH:MM:SS'' or `HHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select SEC_TO_TIME(2378); -> '00:39:38' mysql> select SEC_TO_TIME(2378) + 0; -> 3938 __sec_to_time__ use constant H_TIME_TO_SEC => <<'__time_to_sec__'; TIME_TO_SEC(time): Returns the `time' argument, converted to seconds. mysql> select TIME_TO_SEC('22:23:00'); -> 80580 mysql> select TIME_TO_SEC('00:39:38'); -> 2378 __time_to_sec__ use constant H_DATE_TIME_FUNCTIONS => <<'__date_time_functions__'; Date and Time Functions: dayofweek weekday dayofmonth dayofyear month dayname monthname quarter week year yearweek hour minute second period_add period_diff date_add to_days from_days date_format time_format curdate curtime now unix_timestamp from_unixtime sec_to_time time_to_sec __date_time_functions__ use constant H_DATABASE => <<'__database__'; DATABASE(): Returns the current database name. mysql> select DATABASE(); -> 'test' If there is no current database, `DATABASE()' returns the empty string. __database__ use constant H_USER => <<'__user__'; USER(): SYSTEM_USER(): SESSION_USER(): Returns the current *MySQL* user name. mysql> select USER(); -> 'davida@localhost' In *MySQL* 3.22.11 or later, this includes the client hostname as well as the user name. You can extract just the user name part like this (which works whether or not the value includes a hostname part): mysql> select substring_index(USER(),"@",1); -> 'davida' __user__ use constant H_SYSTEM_USER => H_USER; use constant H_SESSION_USER => H_USER; use constant H_PASSWORD => <<'__password__'; PASSWORD(str): Calculates a password string from the plaintext password `str'. This is the function that is used for encrypting *MySQL* passwords for storage in the `Password' column of the `user' grant table. mysql> select PASSWORD('badpwd'); -> '7f84554057dd964b' `PASSWORD()' encryption is non-reversible. `PASSWORD()' does not perform password encryption in the same way that Unix passwords are encrypted. You should not assume that if your Unix password and your *MySQL* password are the same, `PASSWORD()' will result in the same encrypted value as is stored in the Unix password file. See `ENCRYPT()'. __password__ use constant H_ENCRYPT => <<'__encrypt__'; ENCRYPT(str[,salt]): Encrypt `str' using the Unix `crypt()' system call. The `salt' argument should be a string with two characters. (As of *MySQL* 3.22.16, `salt' may be longer than two characters.) mysql> select ENCRYPT("hello"); -> 'VxuFAJXVARROc' If `crypt()' is not available on your system, `ENCRYPT()' always returns `NULL'. `ENCRYPT()' ignores all but the first 8 characters of `str', at least on some systems. This will be determined by the behavior of the underlying `crypt()' system call. __encrypt__ use constant H_ENCODE => <<'__encode__'; ENCODE(str,pass_str): Encrypt `str' using `pass_str' as the password. To decrypt the result, use `DECODE()'. The results is a binary string of the same length as `string'. If you want to save it in a column, use a `BLOB' column type. __encode__ use constant H_DECODE => <<'__decode__'; DECODE(crypt_str,pass_str): Descrypts the encrypted string `crypt_str' using `pass_str' as the password. `crypt_str' should be a string returned from `ENCODE()'. __decode__ use constant H_MD5 => <<'__md5__'; MD5(string): Calculates a MD5 checksum for the string. Value is returned as a 32 long hex number that may, for example, be used as a hash key. mysql> select MD5("testing") -> 'ae2b1fca515949e5d54fb22b8ed95575' This is an "RSA Data Security, Inc. MD5 Message-Digest Algorithm". __md5__ use constant H_LAST_INSERT_ID => <<'__last_insert_id__'; LAST_INSERT_ID([expr]): Returns the last automatically generated value that was inserted into an `AUTO_INCREMENT' column. *Note `mysql_insert_id()': mysql_insert_id. mysql> select LAST_INSERT_ID(); -> 195 The last ID that was generated is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another `AUTO_INCREMENT' column with a non-magic value (that is, a value that is not `NULL' and not `0'). If `expr' is given as an argument to `LAST_INSERT_ID()' in an `UPDATE' clause, then the value of the argument is returned as a `LAST_INSERT_ID()' value. This can be used to simulate sequences: First create the table: mysql> create table sequence (id int not null); mysql> insert into sequence values (0); Then the table can be used to generate sequence numbers like this: mysql> update sequence set id=LAST_INSERT_ID(id+1); You can generate sequences without calling `LAST_INSERT_ID()', but the utility of using the function this way is that the ID value is maintained in the server as the last automatically generated value. You can retrieve the new ID as you would read any normal `AUTO_INCREMENT' value in *MySQL*. For example, `LAST_INSERT_ID()' (without an argument) will return the new ID. The C API function `mysql_insert_id()' can also be used to get the value. __last_insert_id__ use constant H_FORMAT => <<'__format__'; FORMAT(X,D): Formats the number `X' to a format like `'#,###,###.##'', rounded to `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select FORMAT(12332.123456, 4); -> '12,332.1235' mysql> select FORMAT(12332.1,4); -> '12,332.1000' mysql> select FORMAT(12332.2,0); -> '12,332' __format__ use constant H_VERSION => <<'__version__'; VERSION(): Returns a string indicating the *MySQL* server version. mysql> select VERSION(); -> '3.23.13-log' Note that if your version ends with `-log' this means that logging is enabled. __version__ use constant H_CONNECTION_ID => <<'__connection_id__'; CONNECTION_ID(): Returns the connection id (`thread_id') for the connection. Every connection has its own unique id. mysql> select CONNECTION_ID(); -> 1 __connection_id__ use constant H_GET_LOCK => <<'__get_lock__'; GET_LOCK(str,timeout): Tries to obtain a lock with a name given by the string `str', with a timeout of `timeout' seconds. Returns `1' if the lock was obtained successfully, `0' if the attempt timed out, or `NULL' if an error occurred (such as running out of memory or the thread was killed with `mysqladmin kill'). A lock is released when you execute `RELEASE_LOCK()', execute a new `GET_LOCK()' or the thread terminates. This function can be used to implement application locks or to simulate record locks. It blocks requests by other clients for locks with the same name; clients that agree on a given lock string name can use the string to perform cooperative advisory locking. mysql> select GET_LOCK("lock1",10); -> 1 mysql> select GET_LOCK("lock2",10); -> 1 mysql> select RELEASE_LOCK("lock2"); -> 1 mysql> select RELEASE_LOCK("lock1"); -> NULL Note that the second `RELEASE_LOCK()' call returns `NULL' because the lock `"lock1"' was automatically released by the second `GET_LOCK()' call. __get_lock__ use constant H_RELEASE_LOCK => <<'__release_lock__'; RELEASE_LOCK(str): Releases the lock named by the string `str' that was obtained with `GET_LOCK()'. Returns `1' if the lock was released, `0' if the lock wasn't locked by this thread (in which case the lock is not released) and `NULL' if the named lock didn't exist. The lock will not exist if it was never obtained by a call to `GET_LOCK()' or if it already has been released. __release_lock__ use constant H_BENCHMARK => <<'__benchmark__'; BENCHMARK(count,expr): The `BENCHMARK()' function executes the expression `expr' repeatedly `count' times. It may be used to time how fast *MySQL* processes the expression. The result value is always `0'. The intended use is in the `mysql' client, which reports query execution times. mysql> select BENCHMARK(1000000,encode("hello","goodbye")); +----------------------------------------------+ | BENCHMARK(1000000,encode("hello","goodbye")) | +----------------------------------------------+ | 0 | +----------------------------------------------+ 1 row in set (4.74 sec) The time reported is elapsed time on the client end, not CPU time on the server end. It may be advisable to execute `BENCHMARK()' several times, and interpret the result with regard to how heavily loaded the server machine is. __benchmark__ use constant H_INET_NTOA => <<'__inet_ntoa__'; INET_NTOA(expr): Returns the network address (4 or 8 byte) for the numeric expression. mysql> select INET_NTOA(3520061480); -> "209.207.224.40" __inet_ntoa__ use constant H_INET_ATON => <<'__inet_aton__'; INET_ATON(expr): Returns an integer that represents the numeric value for a network address Addresses may be 4 or 8 byte addresses. mysql> select INET_ATON("209.207.224.40"); -> 3520061480 __inet_aton__ use constant H_MISC_FUNCTIONS => <<'__misc_functions__'; Miscellaneous Functions: database user password encrypt encode decode md5 last_insert_id format version connection_id get_lock release_lock benchmark inet_ntoa inet_aton __misc_functions__ use constant H_COUNT => <<'__count__'; COUNT(expr): Returns a count of the number of non-`NULL' values in the rows retrieved by a `SELECT' statement. mysql> select student.student_name,COUNT(*) from student,course where student.student_id=course.student_id GROUP BY student_name; `COUNT(*)' is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain `NULL' values. `COUNT(*)' is optimized to return very quickly if the `SELECT' retrieves from one table, no other columns are retrieved and there is no `WHERE' clause. For example: mysql> select COUNT(*) from student; COUNT(DISTINCT expr,[expr...]): Returns a count of the number of different values. mysql> select COUNT(DISTINCT results) from student; In *MySQL* you can get the number of distinct expressions combinations by giving a list of expressions. In ANSI SQL you would have to do a concatenation of all expressions inside `CODE(DISTINCT ..)'. __count__ use constant H_AVG => <<'__avg__'; AVG(expr): Returns the average value of `expr'. mysql> select student_name, AVG(test_score) from student GROUP BY student_name; __avg__ use constant H_MIN => <<'__min__'; MIN(expr): MAX(expr): Returns the minimum or maximum value of `expr'. `MIN()' and `MAX()' may take a string argument; in such cases they return the minimum or maximum string value. mysql> select student_name, MIN(test_score), MAX(test_score) from student GROUP BY student_name; __min__ use constant H_MAX => H_MIN; use constant H_SUM => <<'__sum__'; SUM(expr): Returns the sum of `expr'. Note that if the return set has no rows, it returns NULL! __sum__ use constant H_STD => <<'__std__'; STD(expr): STDDEV(expr): Returns the standard deviation of `expr'. This is an extension to ANSI SQL. The `STDDEV()' form of this function is provided for Oracle compatability. __std__ use constant H_STDDEV => H_STD; use constant H_BIT_OR => <<'__bit_or__'; BIT_OR(expr): Returns the bitwise `OR' of all bits in `expr'. The calculation is performed with 64-bit (`BIGINT') precision. __bit_or__ use constant H_BIT_AND => <<'__bit_and__'; BIT_AND(expr): Returns the bitwise `AND' of all bits in `expr'. The calculation is performed with 64-bit (`BIGINT' precision. __bit_and__ use constant H_GROUP_BY_FUNCTIONS => <<'__group_by_functions__'; Group By Functions: *MySQL* has extended the use of `GROUP BY'. You can use columns or calculations in the `SELECT' expressions which don't appear in the `GROUP BY' part. This stands for _any possible value for this group_. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you don't need to group on `customer.name' in the following query: mysql> select order.custid,customer.name,max(payments) from order,customer where order.custid = customer.custid GROUP BY order.custid; In ANSI SQL, you would have to add `customer.name' to the `GROUP BY' clause. In *MySQL*, the name is redundant if you don't run in ANSI mode. Don't use this feature if the columns you omit from the `GROUP BY' part aren't unique in the group! In some cases, you can use `MIN()' and `MAX()' to obtain a specific column value even if it isn't unique. The following gives the value of `column' from the row containing the smallest value in the `sort' column: substr(MIN(concat(sort,space(6-length(sort)),column),7,length(column))) Note that if you are using *MySQL* 3.22 (or earlier) or if you are trying to follow ANSI SQL, you can't use expressions in `GROUP BY' or `ORDER BY' clauses. You can work around this limitation by using an alias for the expression: mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name GROUP BY id,val ORDER BY val; In `MySQL' 3.23 you can do: mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND(); See: count avg min sum std bit_or bit_and __group_by_functions__ use constant H_DATA_TYPES => <<'__data_types__'; Column types ============ *MySQL* supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available and summarizes the storage requirements for each column type, then provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values. The column types supported by *MySQL* are listed below. The following code letters are used in the descriptions: `M' Indicates the maximum display size. The maximum legal display size is 255. `D' Applies to floating-point types and indicates the number of digits following the decimal point. The maximum possible value is 30, but should be no greater than `M'-2. Square brackets (`[' and `]') indicate parts of type specifiers that are optional. Note that if you specify `ZEROFILL' for a column, *MySQL* will automatically add the `UNSIGNED' attribute to the column. `TINYINT[(M)] [UNSIGNED] [ZEROFILL]' A very small integer. The signed range is `-128' to `127'. The unsigned range is `0' to `255'. `SMALLINT[(M)] [UNSIGNED] [ZEROFILL]' A small integer. The signed range is `-32768' to `32767'. The unsigned range is `0' to `65535'. `MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]' A medium-size integer. The signed range is `-8388608' to `8388607'. The unsigned range is `0' to `16777215'. `INT[(M)] [UNSIGNED] [ZEROFILL]' A normal-size integer. The signed range is `-2147483648' to `2147483647'. The unsigned range is `0' to `4294967295'. `INTEGER[(M)] [UNSIGNED] [ZEROFILL]' This is a synonym for `INT'. `BIGINT[(M)] [UNSIGNED] [ZEROFILL]' A large integer. The signed range is `-9223372036854775808' to `9223372036854775807'. The unsigned range is `0' to `18446744073709551615'. Note that all arithmetic is done using signed `BIGINT' or `DOUBLE' values, so you shouldn't use unsigned big integers larger than `9223372036854775807' (63 bits) except with bit functions! Note that `-', `+' and `*' will use `BIGINT' arithmetic when both arguments are `INTEGER' values! This means that if you multiply two big integers (or results from functions that return integers) you may get unexpected results if the result is larger than `9223372036854775807'. `FLOAT(precision) [ZEROFILL]' A floating-point number. Cannot be unsigned. `precision' can be `<=24' for a single precision floating point number and between 25 and 53 for a double precision floating point number. these types are like the `FLOAT' and `DOUBLE' types described immediately below. `FLOAT(X)' have the same ranges as the corresponding `FLOAT' and `DOUBLE' types, but the display size and number of decimals is undefined. In *MySQL* 3.23, this is a true floating point value. In earlier *MySQL* versions, `FLOAT(precision)' always has 2 decimals. This syntax is provided for ODBC compatibility. `FLOAT[(M,D)] [ZEROFILL]' A small (single-precision) floating-point number. Cannot be unsigned. Allowable values are `-3.402823466E+38' to `-1.175494351E-38', `0' and `1.175494351E-38' to `3.402823466E+38'. The M is the display width and D is the number of decimals. `FLOAT' without an argument or with an argument of <= 24 stands for a single-precision floating point number. `DOUBLE[(M,D)] [ZEROFILL]' A normal-size (double-precision) floating-point number. Cannot be unsigned. Allowable values are `-1.7976931348623157E+308' to `-2.2250738585072014E-308', `0' and `2.2250738585072014E-308' to `1.7976931348623157E+308'. The M is the display width and D is the number of decimals. `DOUBLE' without an argument or `FLOAT(X)' where 25 <= X <= 53 stands for a double-precision floating point number. `DOUBLE PRECISION[(M,D)] [ZEROFILL]' `REAL[(M,D)] [ZEROFILL]' These are synonyms for `DOUBLE'. `DECIMAL[(M[,D])] [ZEROFILL]' An unpacked floating-point number. Cannot be unsigned. Behaves like a `CHAR' column: "unpacked" means the number is stored as a string, using one character for each digit of the value. The decimal point, and, for negative numbers, the `-' sign is not counted in M. If `D' is 0, values will have no decimal point or fractional part. The maximum range of `DECIMAL' values is the same as for `DOUBLE', but the actual range for a given `DECIMAL' column may be constrained by the choice of `M' and `D'. If `D' is left out it's set to 0. If `M' is left out it's set to 10. Note that in *MySQL* 3.22 the `M' argument includes the sign and the decimal point. `NUMERIC(M,D) [ZEROFILL]' This is a synonym for `DECIMAL'. `DATE' A date. The supported range is `'1000-01-01'' to `'9999-12-31''. *MySQL* displays `DATE' values in `'YYYY-MM-DD'' format, but allows you to assign values to `DATE' columns using either strings or numbers. `DATETIME' A date and time combination. The supported range is `'1000-01-01 00:00:00'' to `'9999-12-31 23:59:59''. *MySQL* displays `DATETIME' values in `'YYYY-MM-DD HH:MM:SS'' format, but allows you to assign values to `DATETIME' columns using either strings or numbers. `TIMESTAMP[(M)]' A timestamp. The range is `'1970-01-01 00:00:00'' to sometime in the year `2037'. *MySQL* displays `TIMESTAMP' values in `YYYYMMDDHHMMSS', `YYMMDDHHMMSS', `YYYYMMDD' or `YYMMDD' format, depending on whether `M' is `14' (or missing), `12', `8' or `6', but allows you to assign values to `TIMESTAMP' columns using either strings or numbers. A `TIMESTAMP' column is useful for recording the date and time of an `INSERT' or `UPDATE' operation because it is automatically set to the date and time of the most recent operation if you don't give it a value yourself. You can also set it to the current date and time by assigning it a `NULL' value. *Note Date and time types::. `TIME' A time. The range is `'-838:59:59'' to `'838:59:59''. *MySQL* displays `TIME' values in `'HH:MM:SS'' format, but allows you to assign values to `TIME' columns using either strings or numbers. `YEAR[(2|4)]' A year in 2- or 4- digit formats (default is 4-digit). The allowable values are `1901' to `2155', and `0000' in the 4 year format and 1970-2069 if you use the 2 digit format (70-69). *MySQL* displays `YEAR' values in `YYYY' format, but allows you to assign values to `YEAR' columns using either strings or numbers. (The `YEAR' type is new in *MySQL* 3.22.) `[NATIONAL] CHAR(M) [BINARY]' A fixed-length string that is always right-padded with spaces to the specified length when stored. The range of `M' is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. `CHAR' values are sorted and compared in case-insensitive fashion according to the default character set unless the `BINARY' keyword is given. `NATIONAL CHAR' (short form `NCHAR') is the ANSI SQL way to define that a CHAR column should use the default CHARACTER set. This is default in `MySQL'. `CHAR' is a shorthand for `CHARACTER'. *MySQL* allows you to create a column of type `CHAR(0)'. This is mainly useful when you have to be compliant with some old applications that depend on the existence of a column but that do not actually use the value. This is also quite nice when you need a column that only can take 2 values: A `CHAR(0)', that is not defined as `NOT NULL', will only occupy one bit and can only take 2 values: `NULL' or `""'. `[NATIONAL] VARCHAR(M) [BINARY]' A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification). The range of `M' is 1 to 255 characters. `VARCHAR' values are sorted and compared in case-insensitive fashion unless the `BINARY' keyword is given. *Note Silent column changes::. `VARCHAR' is a shorthand for `CHARACTER VARYING'. `TINYBLOB' `TINYTEXT' A `BLOB' or `TEXT' column with a maximum length of 255 (2^8 - 1) characters. *Note Silent column changes::. `BLOB' `TEXT' A `BLOB' or `TEXT' column with a maximum length of 65535 (2^16 - 1) characters. *Note Silent column changes::. `MEDIUMBLOB' `MEDIUMTEXT' A `BLOB' or `TEXT' column with a maximum length of 16777215 (2^24 - 1) characters. *Note Silent column changes::. `LONGBLOB' `LONGTEXT' A `BLOB' or `TEXT' column with a maximum length of 4294967295 (2^32 - 1) characters. *Note Silent column changes::. `ENUM('value1','value2',...)' An enumeration. A string object that can have only one value, chosen from the list of values `'value1'', `'value2'', `...', or `NULL'. An `ENUM' can have a maximum of 65535 distinct values. `SET('value1','value2',...)' A set. A string object that can have zero or more values, each of which must be chosen from the list of values `'value1'', `'value2'', `...' A `SET' can have a maximum of 64 members. __data_types__ use constant H_MYSQL_VARIABLES => <<'__mysql_variables__'; Mysql Variables: ============== *MySQL* supports thread specific variables with the `@variablename' syntax. A variable name may consist of alphanumeric characters from the current character set and also `_', `$', and `.' . The default character set is ISO-8859-1 Latin1; this may be changed with the `--default-character-set' option to `mysqld'. *Note Character sets::. Variables don't have to be initialized. They contain `NULL' by default and can store an integer, real or string value. All variables for a thread are automatically freed when the thread exits. You can set a variable with the `SET' syntax: SET @variable= { integer expression | real expression | string expression } [,@variable= ...]. You can also set a variable in an expression with the `@variable:=expr' syntax: select @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3; +----------------------+------+------+------+ | @t1:=(@t2:=1)+@t3:=4 | @t1 | @t2 | @t3 | +----------------------+------+------+------+ | 5 | 5 | 1 | 4 | +----------------------+------+------+------+ (We had to use the `:=' syntax here, because `=' was reserved for comparisons.) User variables may be used where expressions are allowed. Note that this does not currently include use in contexts where a number is explicitly required, such as in the `LIMIT' clause of a `SELECT' statement, or the `IGNORE number LINES' clause of a `LOAD DATA' statement. *NOTE:* In a `SELECT' statement, each expression is only evaluated when it's sent to the client. This means that one can't in the `HAVING', `GROUP BY' or `ORDER BY' clause refer to an expression that involves variables that are set in the `SELECT' part. For example, the following statement will NOT work as expected: SELECT (@aa:=id) AS a, (@aa+3) AS b FROM table_name HAVING b=5; The reason is that `@aa' will not contain the value of the current row, but the value of `id' for the previous accepted row. __mysql_variables__ use constant H_CREATE_DATABASE => <<'__create_database__'; CREATE DATABASE [IF NOT EXISTS] db_name `CREATE DATABASE' creates a database with the given name. An error occurs if the database already exists and you didn't specify `IF NOT EXISTS'. Databases in *MySQL* are implemented as directories containing files that correspond to tables in the database. Because there are no tables in a database when it is initially created, the `CREATE DATABASE' statement only creates a directory under the *MySQL* data directory. You can also create databases with `mysqladmin'. __create_database__ use constant CREATE_TABLE => <<'__create_table__'; CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)] [table_options] [select_statement] create_definition: col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT] [PRIMARY KEY] [reference_definition] or PRIMARY KEY (index_col_name,...) or KEY [index_name] (index_col_name,...) or INDEX [index_name] (index_col_name,...) or UNIQUE [INDEX] [index_name] (index_col_name,...) or [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...) [reference_definition] or CHECK (expr) type: TINYINT[(length)] [UNSIGNED] [ZEROFILL] or SMALLINT[(length)] [UNSIGNED] [ZEROFILL] or MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL] or INT[(length)] [UNSIGNED] [ZEROFILL] or INTEGER[(length)] [UNSIGNED] [ZEROFILL] or BIGINT[(length)] [UNSIGNED] [ZEROFILL] or REAL[(length,decimals)] [UNSIGNED] [ZEROFILL] or DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL] or FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL] or DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL] or NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL] or CHAR(length) [BINARY] or VARCHAR(length) [BINARY] or DATE or TIME or TIMESTAMP or DATETIME or TINYBLOB or BLOB or MEDIUMBLOB or LONGBLOB or TINYTEXT or TEXT or MEDIUMTEXT or LONGTEXT or ENUM(value1,value2,value3,...) or SET(value1,value2,value3,...) index_col_name: col_name [(length)] reference_definition: REFERENCES tbl_name [(index_col_name,...)] [MATCH FULL | MATCH PARTIAL] [ON DELETE reference_option] [ON UPDATE reference_option] reference_option: RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT table_options: TYPE = {ISAM | MYISAM | HEAP} or AUTO_INCREMENT = # or AVG_ROW_LENGTH = # or CHECKSUM = {0 | 1} or COMMENT = "string" or MAX_ROWS = # or MIN_ROWS = # or PACK_KEYS = {0 | 1} or PASSWORD = "string" or DELAY_KEY_WRITE = {0 | 1} or ROW_FORMAT= { default | dynamic | static | compressed } or RAID_TYPE= {1 | STRIPED | RAID0 } RAID_CHUNKS=# RAID_CHUNKSIZE=#; select_statement: [IGNORE | REPLACE] SELECT ... (Some legal select statement) `CREATE TABLE' creates a table with the given name in the current database. Rules for allowable table names are given in *Note Legal names::. An error occurs if there is no current database or if the table already exists. In *MySQL* 3.22 or later, the table name can be specified as `db_name.tbl_name'. This works whether or not there is a current database. In *MySQL* 3.23, you can use the `TEMPORARY' keyword when you create a table. A temporary table will automatically be deleted if a connection dies and the name is per connection. This means that two different connections can both use the same temporary table name without conflicting with each other or with an existing table of the same name. (The existing table is hidden until the temporary table is deleted). In *MySQL* 3.23 or later, you can use the keywords `IF NOT EXISTS' so that an error does not occur if the table already exists. Note that there is no verification that the table structures are identical. Each table `tbl_name' is represented by some files in the database directory. In the case of MyISAM-type tables you will get: *File* *Purpose* `tbl_name.frm' Table definition (form) file `tbl_name.MYD' Data file `tbl_name.MYI' Index file For more information on the properties of the various column types, see *Note Column types::. * If neither `NULL' nor `NOT NULL' is specified, the column is treated as though `NULL' had been specified. * An integer column may have the additional attribute `AUTO_INCREMENT'. When you insert a value of `NULL' (recommended) or `0' into an `AUTO_INCREMENT' column, the column is set to `value+1', where `value' is the largest value for the column currently in the table. `AUTO_INCREMENT' sequences begin with `1'. *Note `mysql_insert_id()': mysql_insert_id. If you delete the row containing the maximum value for an `AUTO_INCREMENT' column, the value will be reused with an ISAM table but not with a `MyISAM' table. If you delete all rows in the table with `DELETE FROM table_name' (without a `WHERE') in `AUTOCOMMIT' mode, the sequence starts over for both table types. *Note:* There can be only one `AUTO_INCREMENT' column per table, and it must be indexed. *MySQL* 3.23 will also only work properly if the auto_increment column only has positive values. Inserting a negative number is regarded as inserting a very large positive number. This is done to avoid precision problems when numbers 'wrap' over from positive to negative and also to ensure that one doesn't accidently get a auto_increment column that contains 0. To make *MySQL* compatible with some ODBC applications, you can find the last inserted row with the following query: SELECT * FROM tbl_name WHERE auto_col IS NULL * `NULL' values are handled differently for `TIMESTAMP' columns than for other column types. You cannot store a literal `NULL' in a `TIMESTAMP' column; setting the column to `NULL' sets it to the current date and time. Because `TIMESTAMP' columns behave this way, the `NULL' and `NOT NULL' attributes do not apply in the normal way and are ignored if you specify them. On the other hand, to make it easier for *MySQL* clients to use `TIMESTAMP' columns, the server reports that such columns may be assigned `NULL' values (which is true), even though `TIMESTAMP' never actually will contain a `NULL' value. You can see this when you use `DESCRIBE tbl_name' to get a description of your table. Note that setting a `TIMESTAMP' column to `0' is not the same as setting it to `NULL', because `0' is a valid `TIMESTAMP' value. * If no `DEFAULT' value is specified for a column, *MySQL* automatically assigns one. If the column may take `NULL' as a value, the default value is `NULL'. If the column is declared as `NOT NULL', the default value depends on the column type: - For numeric types other than those declared with the `AUTO_INCREMENT' attribute, the default is `0'. For an `AUTO_INCREMENT' column, the default value is the next value in the sequence. - For date and time types other than `TIMESTAMP', the default is the appropriate "zero" value for the type. For the first `TIMESTAMP' column in a table, the default value is the current date and time. *Note Date and time types::. - For string types other than `ENUM', the default value is the empty string. For `ENUM', the default is the first enumeration value. * `KEY' is a synonym for `INDEX'. * In *MySQL*, a `UNIQUE' key can have only distinct values. An error occurs if you try to add a new row with a key that matches an existing row. * A `PRIMARY KEY' is a unique `KEY' with the extra constraint that all key columns must be defined as `NOT NULL'. In *MySQL* the key is named `PRIMARY'. A table can have only one `PRIMARY KEY'. If you don't have a `PRIMARY KEY' and some applications ask for the `PRIMARY KEY' in your tables, *MySQL* will return the first `UNIQUE' key, which doesn't have any `NULL' columns, as the `PRIMARY KEY'. * A `PRIMARY KEY' can be a multiple-column index. However, you cannot create a multiple-column index using the `PRIMARY KEY' key attibute in a column specification. Doing so will mark only that single column as primary. You must use the `PRIMARY KEY(index_col_name, ...)' syntax. * If the `PRIMARY' or `UNIQUE' key consists of only one column and this is of type integer, you can also refer to it as `_rowid' (new in 3.23.11). * If you don't assign a name to an index, the index will be assigned the same name as the first `index_col_name', with an optional suffix (`_2', `_3', `...') to make it unique. You can see index names for a table using `SHOW INDEX FROM tbl_name'. *Note `SHOW': SHOW. * Only the `MyISAM' table type supports indexes on columns that can have `NULL' values. In other cases you must declare such columns `NOT NULL' or an error results. * With `col_name(length)' syntax, you can specify an index which uses only a part of a `CHAR' or `VARCHAR' column. This can make the index file much smaller. *Note Indexes::. * Only the `MyISAM' table type supports indexing on `BLOB' and `TEXT' columns. When putting an index on a `BLOB' or `TEXT' column you MUST always specify the length of the index: CREATE TABLE test (blob_col BLOB, index(blob_col(10))); * When you use `ORDER BY' or `GROUP BY' with a `TEXT' or `BLOB' column, only the first `max_sort_length' bytes are used. *Note `BLOB': BLOB. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. * Each `NULL' column takes one bit extra, rounded up to the nearest byte. * The maximum record length in bytes can be calculated as follows: row length = 1 + (sum of column lengths) + (number of NULL columns + 7)/8 + (number of variable-length columns) * The `table_options' and `SELECT' options is only implemented in *MySQL* 3.23 and above. The different table types are: ISAM The original table handler. *Note ISAM::. MyISAM The new binary portable table handler. *Note MyISAM::. HEAP The data for this table is only stored in memory. *Note HEAP::. BDB or Transaction safe tables *Note BDB::. Berkeley_db *Note Table types::. The other table options are used to optimize the behavior of the table. In most cases, you don't have to specify any of them. The options work for all table types, if not otherwise indicated. `AUTO_INCREMENT'The next auto_increment value you want to set for your table (MyISAM) `AVG_ROW_LENGTH'An approximation of the average row length for your table. You only need to set this for tables with variable size records. `CHECKSUM' Set this to 1 if you want *MySQL* to maintain a checksum for all rows (makes the table a little slower to update but makes it easier to find corrupted tables) (MyISAM) `COMMENT' A 60 character comment for your table `MAX_ROWS' Max number of rows you plan to store in the table `MIN_ROWS' Minimum number of rows you plan to store in the table `PACK_KEYS' Set this to 1 if you want to have smaller index. This usually makes updates slower and reads faster (MyISAM, ISAM). `PASSWORD' Encrypt the `.frm' file with a password. This option doesn't do anything in the standard *MySQL* version. `DELAY_KEY_WRITE'Set this to 1 if want to delay key table updates until the table is closed (MyISAM). `ROW_FORMAT' Defines how the rows should be stored (for the future). When you use a `MyISAM' table, *MySQL* uses the product of `max_rows * avg_row_length' to decide how big the resulting table will be. If you don't specify any of the above options, the maximum size for a table will be 4G (or 2G if your operating systems only supports 2G tables). If you don't use `PACK_KEYS', the default is to only pack strings, not numbers. If you use `PACK_KEYS=1', numbers will be packed as well. When packing binary number keys, *MySQL* will use prefix compression. This means that you will only get a big benefit of this if you have many numbers that are the same. Prefix compression means that every key needs one extra byte to indicate how many bytes of the previous key are the same for the next key (note that the pointer to the row is stored in high-byte-first-order directly after the key, to improve compression. This means that if you have many equal keys on two rows in a row, all following 'same' keys will usually only take 2 bytes (including the pointer to the row). Compare this to the ordinary case where the following keys will take 'storage_size_for_key' + pointer_size (usually 4). On the other hand, if all keys are totally different, you will lose 1 byte per key, if the key isn't a key that can have `NULL' values (In this case the packed key length will be stored in the same byte that is used to mark if a key is `NULL'). * If you specify a `SELECT' after the `CREATE STATEMENT', *MySQL* will create new fields for all elements in the `SELECT'. For example: mysql> CREATE TABLE test (a int not null auto_increment, primary key (a), key(b)) TYPE=HEAP SELECT b,c from test2; This will create a `HEAP' table with 3 columns. Note that the table will automatically be deleted if any errors occur while copying data into the table. * The `RAID_TYPE' option will help you to break the 2G/4G limit on OSes that don't support big files. You can get also more speed from the I/O bottleneck by putting `RAID' directories on different physical disks. `RAID_TYPE' will work on any OS, as long as you have configured *MySQL* with `--with-raid'. For now the only allowed `RAID_TYPE' is `STRIPED' (`1' and `RAID0' are aliases for this). If you specify `RAID_TYPE=STRIPED' for a `MyISAM' table, `MyISAM' will create `RAID_CHUNKS' sub-directories named 00, 01, 02 in the database directory. In each of these directories `MyISAM' will create an `table_name.MYD'. When writing data to the data file, the `RAID' handler will map the first `RAID_CHUNKSIZE' *1024 bytes to the first file, the next `RAID_CHUNKSIZE' *1024 bytes to the next file and so on. __create_table__ use constant H_DROP_DATABASE => <<'__drop_database__'; DROP DATABASE [IF EXISTS] db_name `DROP DATABASE' drops all tables in the database and deletes the database. *Be VERY careful with this command!* `DROP DATABASE' returns the number of files that were removed from the database directory. Normally, this is three times the number of tables, because each table corresponds to a `.MYD' file, a `.MYI' file and a `.frm' file. In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring if the database doesn't exist. You can also drop databases with `mysqladmin'. __drop_database__ use constant H_ALTER_TABLE => <<'__alter_table__'; ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...] alter_specification: ADD [COLUMN] create_definition [FIRST | AFTER column_name ] or ADD [COLUMN] (create_definition, create_definition,...) or ADD INDEX [index_name] (index_col_name,...) or ADD PRIMARY KEY (index_col_name,...) or ADD UNIQUE [index_name] (index_col_name,...) or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT} or CHANGE [COLUMN] old_col_name create_definition or MODIFY [COLUMN] create_definition or DROP [COLUMN] col_name or DROP PRIMARY KEY or DROP INDEX index_name or RENAME [AS] new_tbl_name or table_options `ALTER TABLE' allows you to change the structure of an existing table. For example, you can add or delete columns, create or destroy indexes, change the type of existing columns, or rename columns or the table itself. You can also change the comment for the table and type of the table. *Note `CREATE TABLE': CREATE TABLE. If you use `ALTER TABLE' to change a column specification but `DESCRIBE tbl_name' indicates that your column was not changed, it is possible that *MySQL* ignored your modification for one of the reasons described in *Note Silent column changes::. For example, if you try to change a `VARCHAR' column to `CHAR', *MySQL* will still use `VARCHAR' if the table contains other variable-length columns. `ALTER TABLE' works by making a temporary copy of the original table. The alteration is performed on the copy, then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While `ALTER TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. * To use `ALTER TABLE', you need *select*, *insert*, *delete*, *update*, *create* and *drop* privileges on the table. * `IGNORE' is a *MySQL* extension to ANSI SQL92. It controls how `ALTER TABLE' works if there are duplicates on unique keys in the new table. If `IGNORE' isn't specified, the copy is aborted and rolled back. If `IGNORE' is specified, then for rows with duplicates on a unique key, only the first row is used; the others are deleted. * You can issue multiple `ADD', `ALTER', `DROP' and `CHANGE' clauses in a single `ALTER TABLE' statement. This is a *MySQL* extension to ANSI SQL92, which allows only one of each clause per `ALTER TABLE' statement. * `CHANGE col_name', `DROP col_name' and `DROP INDEX' are *MySQL* extensions to ANSI SQL92. * `MODIFY' is an Oracle extension to `ALTER TABLE'. * The optional word `COLUMN' is a pure noise word and can be omitted. * If you use `ALTER TABLE tbl_name RENAME AS new_name' without any other options, *MySQL* simply renames the files that correspond to the table `tbl_name'. There is no need to create the temporary table. * `create_definition' clauses use the same syntax for `ADD' and `CHANGE' as for `CREATE TABLE'. Note that this syntax includes the column name, not just the column type. *Note `CREATE TABLE': CREATE TABLE. * You can rename a column using a `CHANGE old_col_name create_definition' clause. To do so, specify the old and new column names and the type that the column currently has. For example, to rename an `INTEGER' column from `a' to `b', you can do this: mysql> ALTER TABLE t1 CHANGE a b INTEGER; If you want to change a column's type but not the name, `CHANGE' syntax still requires two column names even if they are the same. For example: mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL; However, as of *MySQL* 3.22.16a, you can also use `MODIFY' to change a column's type without renaming it: mysql> ALTER TABLE t1 MODIFY b BIGINT NOT NULL; * If you use `CHANGE' or `MODIFY' to shorten a column for which an index exists on part of the column (for instance, if you have an index on the first 10 characters of a `VARCHAR' column), you cannot make the column shorter than the number of characters that are indexed. * When you change a column type using `CHANGE' or `MODIFY', *MySQL* tries to convert data to the new type as well as possible. * In *MySQL* 3.22 or later, you can use `FIRST' or `ADD ... AFTER col_name' to add a column at a specific position within a table row. The default is to add the column last. * `ALTER COLUMN' specifies a new default value for a column or removes the old default value. If the old default is removed and the column can be `NULL', the new default is `NULL'. If the column cannot be `NULL', *MySQL* assigns a default value. Default value assignment is described in *Note `CREATE TABLE': CREATE TABLE. * `DROP INDEX' removes an index. This is a *MySQL* extension to ANSI SQL92. * If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well. * `DROP PRIMARY KEY' drops the primary index. If no such index exists, it drops the first `UNIQUE' index in the table. (*MySQL* marks the first `UNIQUE' key as the `PRIMARY KEY' if no `PRIMARY KEY' was specified explicitly.) * With the C API function `mysql_info()', you can find out how many records were copied, and (when `IGNORE' is used) how many records were deleted due to duplication of unique key values. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. Here is an example that shows some of the uses of `ALTER TABLE'. We begin with a table `t1' that is created as shown below: mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10)); To rename the table from `t1' to `t2': mysql> ALTER TABLE t1 RENAME t2; To change column `a' from `INTEGER' to `TINYINT NOT NULL' (leaving the name the same), and to change column `b' from `CHAR(10)' to `CHAR(20)' as well as renaming it from `b' to `c': mysql> ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20); To add a new `TIMESTAMP' column named `d': mysql> ALTER TABLE t2 ADD d TIMESTAMP; To add an index on column `d', and make column `a' the primary key: mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a); To remove column `c': mysql> ALTER TABLE t2 DROP COLUMN c; To add a new `AUTO_INCREMENT' integer column named `c': mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT, ADD INDEX (c); Note that we indexed `c', because `AUTO_INCREMENT' columns must be indexed, and also that we declare `c' as `NOT NULL', because indexed columns cannot be `NULL'. When you add an `AUTO_INCREMENT' column, column values are filled in with sequence numbers for you automatically. Problems with `ALTER TABLE'. ============================ If `ALTER TABLE' dies with an error like this: Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17) The problem may be that *MySQL* has crashed in a previous `ALTER TABLE' and there is an old table named `A-something' or `B-something' lying around. In this case, go to the *MySQL* data directory and delete all files that have names starting with `A-' or `B-'. (You may want to move them elsewhere instead of deleting them). `ALTER TABLE' works the following way: * Create a new table named `A-xxx' with the requested changes. * All rows from the old table are copied to `A-xxx'. * The old table is renamed `B-xxx'. * `A-xxx' is renamed to your old table name. * `B-xxx' is deleted. If something goes wrong with the renaming operation, *MySQL* tries to undo the changes. If something goes seriously wrong (this shouldn't happen, of course), *MySQL* may leave the old table as `B-xxx' but a simple rename should get your data back. Caveat Administrator __alter_table__ use constant H_DROP_TABLE => <<'__drop_table__'; DROP TABLE [IF EXISTS] tbl_name [, tbl_name,...] `DROP TABLE' removes one or more tables. All table data and the table definition are _removed_, so *be careful* with this command! In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring for tables that don't exist. __drop_table__ use constant H_OPTIMIZE_TABLE => <<'__optimize_table__'; OPTIMIZE TABLE tbl_name `OPTIMIZE TABLE' should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have `VARCHAR', `BLOB' or `TEXT' columns). Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. You can use `OPTIMIZE TABLE' to reclaim the unused space. `OPTIMIZE TABLE' works by making a temporary copy of the original table; The old table is copied to the new table (without the unused rows), then the original table is deleted and the new one is renamed. While `OPTIMIZE TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. __optimize_table__ use constant H_CHECK_TABLE => <<'__check_table__'; CHECK TABLE tbl_name[,tbl_name...] [TYPE = QUICK] Check the table(s) for errors. The command returns a table with the following columns: Table Table name Op Always 'check' Msg_type One of `status', `error', `info' or `warning'. Msg_text The message. Note that you can get many rows of information for each checked table. The last one row will be of `Msg_type status' and should normally be `OK'. If you don't get `OK', you should normally run a repair of the table. *Note Table maintenance::. If `TYPE=QUICK' is given then *MySQL* will not scan the rows for table with fixed size records. `CHECK TABLE' only works on `MyISAM' tables and is the same things as running `myisamchk -m table_name' on the table. __check_table__ use constant ANALYZE_TABLE => <<'__analyze_table__'; ANALYZE TABLE tbl_name[,tbl_name...] Analyze and store the key distribution for the table. During the analyze the table is locked with a read lock. This is equivalent of running `myisamchk -a' on the table. *MySQL* uses the stored key distribution to decide in which order tables should be joined when one does a join on something else than a constant. The command returns a table with the following columns: Table Table name Op Always 'analyze Msg_type One of `status', `error', `info' or `warning'. Msg_text The message. You can check the stored key distribution with the `SHOW INDEX' command. __analyze_table__ use constant H_REPAIR_TABLE => <<'__repair_table__'; ANALYZE TABLE tbl_name[,tbl_name...] Analyze and store the key distribution for the table. During the analyze the table is locked with a read lock. This is equivalent of running `myisamchk -a' on the table. *MySQL* uses the stored key distribution to decide in which order tables should be joined when one does a join on something else than a constant. The command returns a table with the following columns: Table Table name Op Always 'analyze Msg_type One of `status', `error', `info' or `warning'. Msg_text The message. You can check the stored key distribution with the `SHOW INDEX' command. __repair_table__ use constant H_DELETE => <<'__delete__'; DELETE [LOW_PRIORITY] FROM tbl_name [WHERE where_definition] [LIMIT rows] `DELETE' deletes rows from `tbl_name' that satisfy the condition given by `where_definition', and returns the number of records deleted. If you issue a `DELETE' with no `WHERE' clause, all rows are deleted. If you do this in `AUTOCOMMIT' mode, *MySQL* does this by recreating the table as an empty table, which is much faster than deleting each row. In this case, `DELETE' returns zero as the number of affected records. (*MySQL* can't return the number of rows that were actually deleted, because the recreate is done without opening the data files. As long as the table definition file `tbl_name.frm' is valid, the table can be recreated this way, even if the data or index files have become corrupted.). If you really want to know how many records are deleted when you are deleting all rows, and are willing to suffer a speed penalty, you can use a `DELETE' statement of this form: mysql> DELETE FROM tbl_name WHERE 1>0; Note that this is MUCH slower than `DELETE FROM tbl_name' with no `WHERE' clause, because it deletes rows one at a time. If you specify the keyword `LOW_PRIORITY', execution of the `DELETE' is delayed until no other clients are reading from the table. Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. To reclaim unused space and reduce file sizes, use the `OPTIMIZE TABLE' statement or the `myisamchk' utility to reorganize tables. `OPTIMIZE TABLE' is easier, but `myisamchk' is faster. The *MySQL*-specific `LIMIT rows' option to `DELETE' tells the server the maximum number of rows to be deleted before control is returned to the client. This can be used to ensure that a specific `DELETE' command doesn't take too much time. You can simply repeat the `DELETE' command until the number of affected rows is less than the `LIMIT' value. __delete__ use constant H_SELECT => <<'__select__'; SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT] [HIGH_PRIORITY] [DISTINCT | DISTINCTROW | ALL] select_expression,... [INTO {OUTFILE | DUMPFILE} 'file_name' export_options] [FROM table_references [WHERE where_definition] [GROUP BY {unsigned_integer | col_name | formula}] [HAVING where_definition] [ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...] [LIMIT [offset,] rows] [PROCEDURE procedure_name] ] `SELECT' is used to retrieve rows selected from one or more tables. `select_expression' indicates the columns you want to retrieve. `SELECT' may also be used to retrieve rows computed without reference to any table. For example: mysql> SELECT 1 + 1; -> 2 All keywords used must be given in exactly the order shown above. For example, a `HAVING' clause must come after any `GROUP BY' clause and before any `ORDER BY' clause. * A `SELECT' expression may be given an alias using `AS'. The alias is used as the expression's column name and can be used with `ORDER BY' or `HAVING' clauses. For example: mysql> select concat(last_name,', ',first_name) AS full_name from mytable ORDER BY full_name; * The `FROM table_references' clause indicates the tables from which to retrieve rows. If you name more than one table, you are performing a join. For information on join syntax, see *Note `JOIN': JOIN. * You can refer to a column as `col_name', `tbl_name.col_name' or `db_name.tbl_name.col_name'. You need not specify a `tbl_name' or `db_name.tbl_name' prefix for a column reference in a `SELECT' statement unless the reference would be ambiguous. See *Note Legal names::, for examples of ambiguity that require the more explicit column reference forms. * A table reference may be aliased using `tbl_name [AS] alias_name'. mysql> select t1.name, t2.salary from employee AS t1, info AS t2 where t1.name = t2.name; mysql> select t1.name, t2.salary from employee t1, info t2 where t1.name = t2.name; * Columns selected for output may be referred to in `ORDER BY' and `GROUP BY' clauses using column names, column aliases or column positions. Column positions begin with 1. mysql> select college, region, seed from tournament ORDER BY region, seed; mysql> select college, region AS r, seed AS s from tournament ORDER BY r, s; mysql> select college, region, seed from tournament ORDER BY 2, 3; To sort in reverse order, add the `DESC' (descending) keyword to the name of the column in the `ORDER BY' clause that you are sorting by. The default is ascending order; this may be specified explicitly using the `ASC' keyword. * The `HAVING' clause can refer to any column or alias named in the `select_expression'. It is applied last, just before items are sent to the client, with no optimization. Don't use `HAVING' for items that should be in the `WHERE' clause. For example, do not write this: mysql> select col_name from tbl_name HAVING col_name > 0; Write this instead: mysql> select col_name from tbl_name WHERE col_name > 0; In *MySQL* 3.22.5 or later, you can also write queries like this: mysql> select user,max(salary) from users group by user HAVING max(salary)>10; In older *MySQL* versions, you can write this instead: mysql> select user,max(salary) AS sum from users group by user HAVING sum>10; * `SQL_SMALL_RESULT', `SQL_BIG_RESULT', `SQL_BUFFER_RESULT', `STRAIGHT_JOIN' and `HIGH_PRIORITY' are *MySQL* extensions to ANSI SQL92. * `HIGH_PRIORITY' will give the `SELECT' higher priority than a statement that updates a table. You should only use this for queries that are very fast and must be done at once. A `SELECT HIGH_PRIORITY' query will run if the table is locked for read even if there is an update statement that is waiting for the table to be free. * `SQL_BIG_RESULT' can be used with `GROUP BY' or `DISTINCT' to tell the optimizer that the result set will have many rows. In this case, *MySQL* will directly use disk based temporary tables if needed. *MySQL* will also in this case prefer sorting to doing a temporary table with a key on the `GROUP BY' elements. * `SQL_BUFFER_RESULT' will put force the result to be put into a temporary table. This will help *MySQL* free the table locks early and will help in cases where it takes a long time to send the result set to the client. * `SQL_SMALL_RESULT', a *MySQL*-specific option, can be used with `GROUP BY' or `DISTINCT' to tell the optimizer that the result set will be small. In this case, *MySQL* will use fast temporary tables to store the resulting table instead of using sorting. In *MySQL* 3.23 this shouldn't normally be needed. * `STRAIGHT_JOIN' forces the optimizer to join the tables in the order in which they are listed in the `FROM' clause. You can use this to speed up a query if the optimizer joins the tables in non-optimal order. *Note `EXPLAIN': EXPLAIN. * The `LIMIT' clause can be used to constrain the number of rows returned by the `SELECT' statement. `LIMIT' takes one or two numeric arguments. If two arguments are given, the first specifies the offset of the first row to return, the second specifies the maximum number of rows to return. The offset of the initial row is 0 (not 1). mysql> select * from table LIMIT 5,10; # Retrieve rows 6-15 If one argument is given, it indicates the maximum number of rows to return. mysql> select * from table LIMIT 5; # Retrieve first 5 rows In other words, `LIMIT n' is equivalent to `LIMIT 0,n'. * The `SELECT ... INTO OUTFILE 'file_name'' form of `SELECT' writes the selected rows to a file. The file is created on the server host, and cannot already exist (among other things, this prevents database tables and files such as `/etc/passwd' from being destroyed). You must have the *file* privilege on the server host to use this form of `SELECT'. `SELECT ... INTO OUTFILE' is the complement of `LOAD DATA INFILE'; the syntax for the `export_options' part of the statement consists of the same `FIELDS' and `LINES' clauses that are used with the `LOAD DATA INFILE' statement. *Note `LOAD DATA': LOAD DATA. In the resulting text file, only the following characters are escaped by the `ESCAPED BY' character: * The `ESCAPED BY' character * The first character in `FIELDS TERMINATED BY' * The first character in `LINES TERMINATED BY' Additionally, `ASCII 0' is converted to `ESCAPED BY' followed by 0 (`ASCII 48'). The reason for the above is that you MUST escape any `FIELDS TERMINATED BY', `ESCAPED BY' or `LINES TERMINATED BY' characters to reliably be able to read the file back. `ASCII 0' is escaped to make it easier to view with some pagers. As the resulting file doesn't have to conform to the SQL syntax, nothing else need be escaped. If you use `INTO DUMPFILE' instead of `INTO OUTFILE' *MySQL* will only write one row into the file, without any column or line terminations and without any escaping. This is useful if you want to store a blob in a file. __select__ use constant H_JOIN => <<'__join__'; *MySQL* supports the following `JOIN' syntaxes for use in `SELECT' statements: table_reference, table_reference table_reference [CROSS] JOIN table_reference table_reference INNER JOIN table_reference join_condition table_reference STRAIGHT_JOIN table_reference table_reference LEFT [OUTER] JOIN table_reference join_condition table_reference LEFT [OUTER] JOIN table_reference table_reference NATURAL [LEFT [OUTER]] JOIN table_reference { oj table_reference LEFT OUTER JOIN table_reference ON conditional_expr } Where `table_reference' is defined as table_name [[AS] alias] [USE INDEX (key_list)] [IGNORE INDEX (key_list)] and `join_condition' is defined as ON conditional_expr | USING (column_list) Note that in version before 3.23.16 the `INNER JOIN' didn't take a join condition! The last `LEFT OUTER JOIN' syntax shown above exists only for compatibility with ODBC. * A table reference may be aliased using `tbl_name AS alias_name' or `tbl_name alias_name'. mysql> select t1.name, t2.salary from employee AS t1, info AS t2 where t1.name = t2.name; * `INNER JOIN' and `,' (comma) are semantically equivalent. Both do a full join between the tables used. Normally, you specify how the tables should be linked in the `WHERE' condition. * The `ON' conditional is any conditional of the form that may be used in a `WHERE' clause. * If there is no matching record for the right table in the `ON' or `USING' part in a `LEFT JOIN', a row with all columns set to `NULL' is used for the right table. You can use this fact to find records in a table that have no counterpart in another table: mysql> select table1.* from table1 LEFT JOIN table2 ON table1.id=table2.id where table2.id is NULL; This example finds all rows in `table1' with an `id' value that is not present in `table2' (i.e., all rows in `table1' with no corresponding row in `table2'). This assumes that `table2.id' is declared `NOT NULL', of course. * The `USING' `(column_list)' clause names a list of columns that must exist in both tables. A `USING' clause such as: A LEFT JOIN B USING (C1,C2,C3,...) is defined to be semantically identical to an `ON' expression like this: A.C1=B.C1 AND A.C2=B.C2 AND A.C3=B.C3,... * The `NATURAL [LEFT] JOIN' of two tables is defined to be semantically equivalent to a `INNER JOIN' or a `LEFT JOIN' with a `USING' clause that names all columns that exist in both tables. * `STRAIGHT_JOIN' is identical to `JOIN', except that the left table is always read before the right table. This can be used for those (few) cases where the join optimizer puts the tables in the wrong order. * As of *MySQL* 3.23.12, you can give hints about which index *MySQL* should use when retrieving information from a table. This is useful if `EXPLAIN' shows that *MySQL* is using the wrong index. By specifying `USE INDEX (key_list)', you can tell *MySQL* to use only one of the specified indexes to find rows in the table. The alternative syntax `IGNORE INDEX (key_list)' can be used to tell *MySQL* to not use some particular index. Some examples: mysql> select * from table1,table2 where table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 USING (id); mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id LEFT JOIN table3 ON table2.id=table3.id; mysql> select * from table1 USE INDEX (key1,key2) WHERE key1=1 and key2=2 AND key3=3; mysql> select * from table1 IGNORE INDEX (key3) WHERE key1=1 and key2=2 AND key3=3; __join__ use constant H_INSERT => <<'__insert__'; INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] VALUES (expression,...),(...),... INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] SELECT ... INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name SET col_name=expression, col_name=expression, ... `INSERT' inserts new rows into an existing table. The `INSERT ... VALUES' form of the statement inserts rows based on explicitly-specified values. The `INSERT ... SELECT' form inserts rows selected from another table or tables. The `INSERT ... VALUES' form with multiple value lists is supported in *MySQL* 3.22.5 or later. The `col_name=expression' syntax is supported in *MySQL* 3.22.10 or later. `tbl_name' is the table into which rows should be inserted. The column name list or the `SET' clause indicates which columns the statement specifies values for. * If you specify no column list for `INSERT ... VALUES' or `INSERT ... SELECT', values for all columns must be provided in the `VALUES()' list or by the `SELECT'. If you don't know the order of the columns in the table, use `DESCRIBE tbl_name' to find out. * Any column not explicitly given a value is set to its default value. For example, if you specify a column list that doesn't name all the columns in the table, unnamed columns are set to their default values. Default value assignment is described in *Note `CREATE TABLE': CREATE TABLE. * An `expression' may refer to any column that was set earlier in a value list. For example, you can say this: mysql> INSERT INTO tbl_name (col1,col2) VALUES(15,col1*2); But not this: mysql> INSERT INTO tbl_name (col1,col2) VALUES(col2*2,15); * If you specify the keyword `LOW_PRIORITY', execution of the `INSERT' is delayed until no other clients are reading from the table. In this case the client has to wait until the insert statement is completed, which may take a long time if the table is in heavy use. This is in contrast to `INSERT DELAYED' which lets the client continue at once. * If you specify the keyword `IGNORE' in an `INSERT' with many value rows, any rows which duplicate an existing `PRIMARY' or `UNIQUE' key in the table are ignored and are not inserted. If you do not specify `IGNORE', the insert is aborted if there is any row that duplicates an existing key value. You can check with the C API function `mysql_info()' how many rows were inserted into the table. * If *MySQL* was configured using the `DONT_USE_DEFAULT_FIELDS' option, `INSERT' statements generate an error unless you explicitly specify values for all columns that require a non-`NULL' value. *Note `configure' options: configure options. * The following conditions hold for a `INSERT INTO ... SELECT' statement: - The query cannot contain an `ORDER BY' clause. - The target table of the `INSERT' statement cannot appear in the `FROM' clause of the `SELECT' part of the query, because it's forbidden in ANSI SQL to `SELECT' from the same table into which you are `INSERT'ing. (The problem is that the `SELECT' possibly would find records that were inserted earlier during the same run. When using sub-select clauses, the situation could easily be very confusing!) - `AUTO_INCREMENT' columns work as usual. If you use `INSERT ... SELECT' or a `INSERT ... VALUES' statement with multiple value lists, you can use the C API function `mysql_info()' to get information about the query. The format of the information string is shown below: Records: 100 Duplicates: 0 Warnings: 0 `Duplicates' indicates the number of rows that couldn't be inserted because they would duplicate some existing unique index value. `Warnings' indicates the number of attempts to insert column values that were problematic in some way. Warnings can occur under any of the following conditions: * Inserting `NULL' into a column that has been declared `NOT NULL'. The column is set to its default value. * Setting a numeric column to a value that lies outside the column's range. The value is clipped to the appropriate endpoint of the range. * Setting a numeric column to a value such as `'10.34 a''. The trailing garbage is stripped and the remaining numeric part is inserted. If the value doesn't make sense as a number at all, the column is set to `0'. * Inserting a string into a `CHAR', `VARCHAR', `TEXT' or `BLOB' column that exceeds the column's maximum length. The value is truncated to the column's maximum length. * Inserting a value into a date or time column that is illegal for the column type. The column is set to the appropriate "zero" value for the type. The `DELAYED' option for the `INSERT' statement is a *MySQL*-specific option that is very useful if you have clients that can't wait for the `INSERT' to complete. This is a common problem when you use *MySQL* for logging and you also periodically run `SELECT' statements that take a long time to complete. `DELAYED' was introduced in *MySQL* 3.22.15. It is a *MySQL* extension to ANSI SQL92. When you use `INSERT DELAYED', the client will get an ok at once and the row will be inserted when the table is not in use by any other thread. Another major benefit of using `INSERT DELAYED' is that inserts from many clients are bundled together and written in one block. This is much faster than doing many separate inserts. Note that currently the queued rows are only stored in memory until they are inserted into the table. This means that if you kill `mysqld' the hard way (`kill -9') or if `mysqld' dies unexpectedly, any queued rows that weren't written to disk are lost! The following describes in detail what happens when you use the `DELAYED' option to `INSERT' or `REPLACE'. In this description, the "thread" is the thread that received an `INSERT DELAYED' command and "handler" is the thread that handles all `INSERT DELAYED' statements for a particular table. * When a thread executes a `DELAYED' statement for a table, a handler thread is created to process all `DELAYED' statements for the table, if no such handler already exists. * The thread checks whether or not the handler has acquired a `DELAYED' lock already; if not, it tells the handler thread to do so. The `DELAYED' lock can be obtained even if other threads have a `READ' or `WRITE' lock on the table. However, the handler will wait for all `ALTER TABLE' locks or `FLUSH TABLES' to ensure that the table structure is up to date. * The thread executes the `INSERT' statement but instead of writing the row to the table it puts a copy of the final row into a queue that is managed by the handler thread. Any syntax errors are noticed by the thread and reported to the client program. * The client can't report the number of duplicates or the `AUTO_INCREMENT' value for the resulting row; it can't obtain them from the server, because the `INSERT' returns before the insert operation has been completed. If you use the C API, the `mysql_info()' function doesn't return anything meaningful, for the same reason. * The update log is updated by the handler thread when the row is inserted into the table. In case of multiple-row inserts, the update log is updated when the first row is inserted. * After every `delayed_insert_limit' rows are written, the handler checks whether or not any `SELECT' statements are still pending. If so, it allows these to execute before continuing. * When the handler has no more rows in its queue, the table is unlocked. If no new `INSERT DELAYED' commands are received within `delayed_insert_timeout' seconds, the handler terminates. * If more than `delayed_queue_size' rows are pending already in a specific handler queue, the thread waits until there is room in the queue. This is useful to ensure that the `mysqld' server doesn't use all memory for the delayed memory queue. * The handler thread will show up in the *MySQL* process list with `delayed_insert' in the `Command' column. It will be killed if you execute a `FLUSH TABLES' command or kill it with `KILL thread_id'. However, it will first store all queued rows into the table before exiting. During this time it will not accept any new `INSERT' commands from another thread. If you execute an `INSERT DELAYED' command after this, a new handler thread will be created. * Note that the above means that `INSERT DELAYED' commands have higher priority than normal `INSERT' commands if there is an `INSERT DELAYED' handler already running! Other update commands will have to wait until the `INSERT DELAYED' queue is empty, someone kills the handler thread (with `KILL thread_id') or someone executes `FLUSH TABLES'. * The following status variables provide information about `INSERT DELAYED' commands: `Delayed_insert_threads'Number of handler threads `Delayed_writes' Number of rows written with `INSERT DELAYED' `Not_flushed_delayed_rows'Number of rows waiting to be written You can view these variables by issuing a `SHOW STATUS' statement or by executing a `mysqladmin extended-status' command. Note that `INSERT DELAYED' is slower than a normal INSERT if the table is not in use. There is also the additional overhead for the server to handle a separate thread for each table on which you use `INSERT DELAYED'. This means that you should only use `INSERT DELAYED' when you are really sure you need it! __insert__ use constant H_REPLACE => <<'__replace__'; REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] VALUES (expression,...) REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] SELECT ... REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name SET col_name=expression, col_name=expression,... `REPLACE' works exactly like `INSERT', except that if an old record in the table has the same value as a new record on a unique index, the old record is deleted before the new record is inserted. __replace__ use constant H_LOAD_DATA => <<'__load_data__'; LOAD DATA [LOW_PRIORITY] [LOCAL] INFILE 'file_name.txt' [REPLACE | IGNORE] INTO TABLE tbl_name [FIELDS [TERMINATED BY '\t'] [OPTIONALLY] ENCLOSED BY ''] [ESCAPED BY '\\' ]] [LINES TERMINATED BY '\n'] [IGNORE number LINES] [(col_name,...)] The `LOAD DATA INFILE' statement reads rows from a text file into a table at a very high speed. If the `LOCAL' keyword is specified, the file is read from the client host. If `LOCAL' is not specified, the file must be located on the server. (`LOCAL' is available in *MySQL* 3.22.6 or later.) For security reasons, when reading text files located on the server, the files must either reside in the database directory or be readable by all. Also, to use `LOAD DATA INFILE' on server files, you must have the *file* privilege on the server host. *Note Privileges provided::. If you specify the keyword `LOW_PRIORITY', execution of the `LOAD DATA' statement is delayed until no other clients are reading from the table. Using `LOCAL' will be a bit slower than letting the server access the files directly, because the contents of the file must travel from the client host to the server host. On the other hand, you do not need the *file* privilege to load local files. You can also load data files by using the `mysqlimport' utility; it operates by sending a `LOAD DATA INFILE' command to the server. The `--local' option causes `mysqlimport' to read data files from the client host. You can specify the `--compress' option to get better performance over slow networks if the client and server support the compressed protocol. When locating files on the server host, the server uses the following rules: * If an absolute pathname is given, the server uses the pathname as is. * If a relative pathname with one or more leading components is given, the server searches for the file relative to the server's data directory. * If a filename with no leading components is given, the server looks for the file in the database directory of the current database. Note that these rules mean a file given as `./myfile.txt' is read from the server's data directory, whereas a file given as `myfile.txt' is read from the database directory of the current database. For example, the following `LOAD DATA' statement reads the file `data.txt' from the database directory for `db1' because `db1' is the current database, even though the statement explicitly loads the file into a table in the `db2' database: mysql> USE db1; mysql> LOAD DATA INFILE "data.txt" INTO TABLE db2.my_table; The `REPLACE' and `IGNORE' keywords control handling of input records that duplicate existing records on unique key values. If you specify `REPLACE', new rows replace existing rows that have the same unique key value. If you specify `IGNORE', input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. If you load data from a local file using the `LOCAL' keyword, the server has no way to stop transmission of the file in the middle of the operation, so the default bahavior is the same as if `IGNORE' is specified. `LOAD DATA INFILE' is the complement of `SELECT ... INTO OUTFILE'. *Note `SELECT': SELECT. To write data from a database to a file, use `SELECT ... INTO OUTFILE'. To read the file back into the database, use `LOAD DATA INFILE'. The syntax of the `FIELDS' and `LINES' clauses is the same for both commands. Both clauses are optional, but `FIELDS' must precede `LINES' if both are specified. If you specify a `FIELDS' clause, each of its subclauses (`TERMINATED BY', `[OPTIONALLY] ENCLOSED BY' and `ESCAPED BY') is also optional, except that you must specify at least one of them. If you don't specify a `FIELDS' clause, the defaults are the same as if you had written this: FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\' If you don't specify a `LINES' clause, the default is the same as if you had written this: LINES TERMINATED BY '\n' __load_data__ use constant H_UPDATE => <<'__update__'; UPDATE [LOW_PRIORITY] [IGNORE] tbl_name SET col_name1=expr1,col_name2=expr2,... [WHERE where_definition] [LIMIT #] `UPDATE' updates columns in existing table rows with new values. The `SET' clause indicates which columns to modify and the values they should be given. The `WHERE' clause, if given, specifies which rows should be updated. Otherwise all rows are updated. If you specify the keyword `LOW_PRIORITY', execution of the `UPDATE' is delayed until no other clients are reading from the table. If you specify the keyword `IGNORE', the update statement will not abort even if we get duplicate key errors during the update. Rows that would cause conflicts will not be updated. If you access a column from `tbl_name' in an expression, `UPDATE' uses the current value of the column. For example, the following statement sets the `age' column to one more than its current value: mysql> UPDATE persondata SET age=age+1; `UPDATE' assignments are evaluated from left to right. For example, the following statement doubles the `age' column, then increments it: mysql> UPDATE persondata SET age=age*2, age=age+1; If you set a column to the value it currently has, *MySQL* notices this and doesn't update it. `UPDATE' returns the number of rows that were actually changed. In *MySQL* 3.22 or later, the C API function `mysql_info()' returns the number of rows that were matched and updated and the number of warnings that occurred during the `UPDATE'. In *MySQL* 3.23 you can use `LIMIT #' to ensure that only a given number of rows are changed. __update__ use constant H_USE => <<'__use__'; USE db_name The `USE db_name' statement tells *MySQL* to use the `db_name' database as the default database for subsequent queries. The database remains current until the end of the session, or until another `USE' statement is issued: mysql> USE db1; mysql> SELECT count(*) FROM mytable; # selects from db1.mytable mysql> USE db2; mysql> SELECT count(*) FROM mytable; # selects from db2.mytable Making a particular database current by means of the `USE' statement does not preclude you from accessing tables in other databases. The example below accesses the `author' table from the `db1' database and the `editor' table from the `db2' database: mysql> USE db1; mysql> SELECT author_name,editor_name FROM author,db2.editor WHERE author.editor_id = db2.editor.editor_id; The `USE' statement is provided for Sybase compatibility. __use__ use constant H_FLUSH => <<'__flush__'; FLUSH flush_option [,flush_option] You should use the `FLUSH' command if you want to clear some of the internal caches *MySQL* uses. To execute `FLUSH', you must have the *reload* privilege. `flush_option' can be any of the following: `HOSTS' Empties the host cache tables. You should flush the host tables if some of your hosts change IP number or if you get the error message `Host ... is blocked'. When more than `max_connect_errors' errors occur in a row for a given host while connection to the *MySQL* server, *MySQL* assumes something is wrong and blocks the host from further connection requests. Flushing the host tables allows the host to attempt to connect again. *Note Blocked host::.) You can start `mysqld' with `-O max_connection_errors=999999999' to avoid this error message. `LOGS' Closes and reopens the standard and update log files. If you have specified the update log file without an extension, the extension number of the new update log file will be incremented by one relative to the previous file. If you have used an extension in the file name, *MySQL* will close and reopen the update log file. *Note Update log::. `PRIVILEGES'Reloads the privileges from the grant tables in the `mysql' database. `TABLES' Closes all open tables. `TABLES Closes all open tables and locks all tables for all WITH READ databases with a read until one executes `UNLOCK TABLES'. LOCK' `STATUS' Resets most status variables to zero. You can also access each of the commands shown above with the `mysqladmin' utility, using the `flush-hosts', `flush-logs', `reload' or `flush-tables' commands. __flush__ use constant H_KILL => <<'__kill__'; KILL thread_id Each connection to `mysqld' runs in a separate thread. You can see which threads are running with the `SHOW PROCESSLIST' command, and kill a thread with the `KILL thread_id' command. If you have the *process* privilege, you can see and kill all threads. Otherwise, you can see and kill only your own threads. You can also use the `mysqladmin processlist' and `mysqladmin kill' commands to examine and kill threads. __kill__ use constant H_SHOW => <<'__show__'; SHOW DATABASES [LIKE wild] SHOW TABLES [FROM db_name] [LIKE wild] SHOW COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] SHOW INDEX FROM tbl_name [FROM db_name] SHOW TABLE STATUS [FROM db_name] [LIKE wild] SHOW STATUS [LIKE wild] SHOW VARIABLES [LIKE wild] SHOW [FULL] PROCESSLIST SHOW GRANTS FOR user `SHOW' provides information about databases, tables, columns or status information about the server. If the `LIKE wild' part is used, the `wild' string can be a string that uses the SQL `%' and `_' wildcard characters. __show__ use constant H_EXPLAIN => <<'__explain__'; EXPLAIN tbl_name EXPLAIN SELECT select_options `EXPLAIN tbl_name' is a synonym for `DESCRIBE tbl_name' or `SHOW COLUMNS FROM tbl_name'. When you precede a `SELECT' statement with the keyword `EXPLAIN', *MySQL* explains how it would process the `SELECT', providing information about how tables are joined and in which order. With the help of `EXPLAIN', you can see when you must add indexes to tables to get a faster `SELECT' that uses indexes to find the records. You can also see if the optimizer joins the tables in an optimal order. To force the optimizer to use a specific join order for a `SELECT' statement, add a `STRAIGHT_JOIN' clause. For non-simple joins, `EXPLAIN' returns a row of information for each table used in the `SELECT' statement. The tables are listed in the order they would be read. *MySQL* resolves all joins using a single-sweep multi-join method. This means that *MySQL* reads a row from the first table, then finds a matching row in the second table, then in the third table and so on. When all tables are processed, it outputs the selected columns and backtracks through the table list until a table is found for which there are more matching rows. The next row is read from this table and the process continues with the next table. Output from `EXPLAIN' includes the following columns: `table' The table to which the row of output refers. `type' The join type. Information about the various types is given below. `possible_keys' The `possible_keys' column indicates which indexes *MySQL* could use to find the rows in this table. Note that this column is totally independent of the order of the tables. That means that some of the keys in possible_keys may not be useable in practice with the generated table order. If this column is empty, there are no relevant indexes. In this case, you may be able to improve the performance of your query by examining the `WHERE' clause to see if it refers to some column or columns that would be suitable for indexing. If so, create an appropriate index and check the query with `EXPLAIN' again. *Note ALTER TABLE::. To see what indexes a table has, use `SHOW INDEX FROM tbl_name'. `key' The `key' column indicates the key that *MySQL* actually decided to use. The key is `NULL' if no index was chosen. If *MySQL* chooses the wrong index, you can probably force *MySQL* to use another index by using `myisamchk --analyze', *Note myisamchk syntax::, or by using `USE INDEX/IGNORE INDEX'. *Note JOIN::. `key_len' The `key_len' column indicates the length of the key that *MySQL* decided to use. The length is `NULL' if the `key' is `NULL'. Note that this tell us how many parts of a multi-part key *MySQL* will actually use. `ref' The `ref' column shows which columns or constants are used with the `key' to select rows from the table. `rows' The `rows' column indicates the number of rows *MySQL* believes it must examine to execute the query. `Extra' This column contains additional information of how *MySQL* will resolve the query. Here follows an explanation of the different text strings that can be found in this column: `Not exists' *MySQL* was able to do a `LEFT JOIN' optimization on the query and will not examine more rows in this table for a row combination after it founds one rows that matches the `LEFT JOIN' criteria. ``range checked for each record (index map: #)'' *MySQL* didn't find a real good index to use. It will instead for each row combination in the preceding tables do a check which index to use (if any) use this index to retrieve the rows from the table. This isn't very fast but is of course faster than having to do a join without an index. `Using filesort' *MySQL* will need to do an extra pass to find out how to retrieve the rows in sorted order. The sort is done by going through all rows according to the `join type' and storing the sort key + pointer to the row for all rows that match the `WHERE'. Then the keys are sorted. Finally the rows are retrieved in sorted order. `Using index' The column information is retrieved from the table using only information in the index tree without having to do an additional seek to read the actually row. This can be done when all the used columns for the table are part of the same index. `Using temporary' To be able to resolve the query *MySQL* will need to create a temporary table to hold the result. This typically happens if you do an `ORDER BY' on a different column set than you did an `GROUP BY' on. `Where used' A `WHERE' clause will be used to restrict which rows will be matched against the next table or sent to the client. If you don't have this information and the the table is of type `ALL' or `index' you may have something wrong in your query (if you don't intend to fetch/examine all rows from the table). If you want to get your queries as fast as possible, you should look out for `Using filesort' and `Using temporary'. The different join types are listed below, ordered from best to worst type: `system' The table has only one row (= system table). This is a special case of the `const' join type. `const' The table has at most one matching row, which will be read at the start of the query. Because there is only one row, values from the column in this row can be regarded as constants by the rest of the optimizer. `const' tables are very fast as they are read only once! `eq_ref' One row will be read from this table for each combination of rows from the previous tables. This the best possible join type, other than the `const' types. It is used when all parts of an index are used by the join and the index is `UNIQUE' or a `PRIMARY KEY'. `ref' All rows with matching index values will be read from this table for each combination of rows from the previous tables. `ref' is used if the join uses only a leftmost prefix of the key, or if the key is not `UNIQUE' or a `PRIMARY KEY' (in other words, if the join cannot select a single row based on the key value). If the key that is used matches only a few rows, this join type is good. `range' Only rows that are in a given range will be retrieved, using an index to select the rows. The `ref' column indicates which index is used. `index' This is the same as `ALL', except that only the index tree is scanned. This is usually faster than `ALL', as the index file is usually smaller than the data file. `ALL' A full table scan will be done for each combination of rows from the previous tables. This is normally not good if the table is the first table not marked `const', and usually *very* bad in all other cases. You normally can avoid `ALL' by adding more indexes, so that the row can be retrieved based on constant values or column values from earlier tables. You can get a good indication of how good a join is by multiplying all values in the `rows' column of the `EXPLAIN' output. This should tell you roughly how many rows *MySQL* must examine to execute the query. This number is also used when you restrict queries with the `max_join_size' variable. __explain__ use constant H_DESCRIBE => <<'__describe__'; {DESCRIBE | DESC} tbl_name {col_name | wild} `DESCRIBE' provides information about a table's columns. `col_name' may be a column name or a string containing the SQL `%' and `_' wildcard characters. __describe__ use constant H_LOCK => <<'__lock__'; LOCK TABLES tbl_name [AS alias] {READ | [READ LOCAL] | [LOW_PRIORITY] WRITE} [, tbl_name {READ | [LOW_PRIORITY] WRITE} ...] ... UNLOCK TABLES `LOCK TABLES' locks tables for the current thread. `UNLOCK TABLES' releases any locks held by the current thread. All tables that are locked by the current thread are automatically unlocked when the thread issues another `LOCK TABLES', or when the connection to the server is closed. If a thread obtains a `READ' lock on a table, that thread (and all other threads) can only read from the table. If a thread obtains a `WRITE' lock on a table, then only the thread holding the lock can `READ' from or `WRITE' to the table. Other threads are blocked. The difference between `READ LOCAL' and `READ' is that `READ LOCAL' allows non-conflicting `INSERT' statements to execute while the lock is held. This can't however be used if you are going to manipulate the database files outside *MySQL* while you hold the lock. Each thread waits (without timing out) until it obtains all the locks it has requested. `WRITE' locks normally have higher priority than `READ' locks, to ensure that updates are processed as soon as possible. This means that if one thread obtains a `READ' lock and then another thread requests a `WRITE' lock, subsequent `READ' lock requests will wait until the `WRITE' thread has gotten the lock and released it. You can use `LOW_PRIORITY WRITE' locks to allow other threads to obtain `READ' locks while the thread is waiting for the `WRITE' lock. You should only use `LOW_PRIORITY WRITE' locks if you are sure that there will eventually be a time when no threads will have a `READ' lock. When you use `LOCK TABLES', you must lock all tables that you are going to use and you must use the same alias that you are going to use in your queries! If you are using a table multiple times in a query (with aliases), you must get a lock for each alias! This policy ensures that table locking is deadlock free. Note that you should *NOT* lock any tables that you are using with `INSERT DELAYED'. This is because that in this case the `INSERT' is done by a separate thread. Normally, you don't have to lock tables, as all single `UPDATE' statements are atomic; no other thread can interfere with any other currently executing SQL statement. There are a few cases when you would like to lock tables anyway: __lock__ use constant H_SET => <<'__set__'; SET [OPTION] SQL_VALUE_OPTION= value, ... `SET OPTION' sets various options that affect the operation of the server or your client. Any option you set remains in effect until the current session ends, or until you set the option to a different value. `CHARACTER SET character_set_name | DEFAULT' This maps all strings from and to the client with the given mapping. Currently the only option for `character_set_name' is `cp1251_koi8', but you can easily add new mappings by editing the `sql/convert.cc' file in the *MySQL* source distribution. The default mapping can be restored by using a `character_set_name' value of `DEFAULT'. Note that the syntax for setting the `CHARACTER SET' option differs from the syntax for setting the other options. `PASSWORD = PASSWORD('some password')' Set the password for the current user. Any non-anonymous user can change his own password! `PASSWORD FOR user = PASSWORD('some password')' Set the password for a specific user on the current server host. Only a user with access to the `mysql' database can do this. The user should be given in `user@hostname' format, where `user' and `hostname' are exactly as they are listed in the `User' and `Host' columns of the `mysql.user' table entry. For example, if you had an entry with `User' and `Host' fields of `'bob'' and `'%.loc.gov'', you would write: mysql> SET PASSWORD FOR bob@"%.loc.gov" = PASSWORD("newpass"); or mysql> UPDATE mysql.user SET password=PASSWORD("newpass") where user="bob' and host="%.loc.gov"; `SQL_AUTO_IS_NULL = 0 | 1' If set to `1' (default) then one can find the last inserted row for a table with an auto_increment row with the following construct: `WHERE auto_increment_column IS NULL'. This is used by some ODBC programs like Access. `SET AUTOCOMMIT= 0 | 1' If set to `1' all changes to a table will be done at once. To start an multi command transaction you have to use the `BEGIN' statement. *Note COMMIT::. If set to `0' you have to use `COMMIT' / `ROLLBACK' to accept/revoke that transaction. *Note COMMIT::. Note that when you change from not `AUTOCOMMIT' mode to `AUTOCOMMIT' mode, *MySQL* will do an automatic `COMMIT' on any open transactions. `SQL_BIG_TABLES = 0 | 1' If set to `1', all temporary tables are stored on disk rather than in memory. This will be a little slower, but you will not get the error `The table tbl_name is full' for big `SELECT' operations that require a large temporary table. The default value for a new connection is `0' (i.e., use in-memory temporary tables). `SQL_BIG_SELECTS = 0 | 1' If set to `0', *MySQL* will abort if a `SELECT' is attempted that probably will take a very long time. This is useful when an inadvisable `WHERE' statement has been issued. A big query is defined as a `SELECT' that probably will have to examine more than `max_join_size' rows. The default value for a new connection is `1' (which will allow all `SELECT' statements). `SQL_BUFFER_RESULT = 0 | 1' `SQL_BUFFER_RESULT' will force the result from `SELECT''s to be put into a temporary table. This will help *MySQL* free the table locks early and will help in cases where it takes a long time to send the result set to the client. `SQL_LOW_PRIORITY_UPDATES = 0 | 1' If set to `1', all `INSERT', `UPDATE', `DELETE' and and `LOCK TABLE WRITE' statements wait until there is no pending `SELECT' or `LOCK TABLE READ' on the affected table. `SQL_MAX_JOIN_SIZE = value | DEFAULT' Don't allow `SELECT''s that will probably need to examine more than `value' row combinations. By setting this value, you can catch `SELECT''s where keys are not used properly and that would probably take a long time. Setting this to a value other than `DEFAULT' will reset the `SQL_BIG_SELECTS' flag. If you set the `SQL_BIG_SELECTS' flag again, the `SQL_MAX_JOIN_SIZE' variable will be ignored. You can set a default value for this variable by starting `mysqld' with `-O max_join_size=#'. `SQL_SAFE_MODE = 0 | 1' If set to `1', *MySQL* will abort if a `UPDATE' or `DELETE' is attempted that doesn't use a key or `LIMIT' in the `WHERE' clause. This makes it possible to catch wrong updates when creating SQL commands by hand. `SQL_SELECT_LIMIT = value | DEFAULT' The maximum number of records to return from `SELECT' statements. If a `SELECT' has a `LIMIT' clause, the `LIMIT' takes precedence over the value of `SQL_SELECT_LIMIT'. The default value for a new connection is "unlimited". If you have changed the limit, the default value can be restored by using a `SQL_SELECT_LIMIT' value of `DEFAULT'. `SQL_LOG_OFF = 0 | 1' If set to `1', no logging will be done to the standard log for this client, if the client has the *process* privilege. This does not affect the update log! `SQL_LOG_UPDATE = 0 | 1' If set to `0', no logging will be done to the update log for the client, if the client has the *process* privilege. This does not affect the standard log! `TIMESTAMP = timestamp_value | DEFAULT' Set the time for this client. This is used to get the original timestamp if you use the update log to restore rows. `LAST_INSERT_ID = #' Set the value to be returned from `LAST_INSERT_ID()'. This is stored in the update log when you use `LAST_INSERT_ID()' in a command that updates a table. `INSERT_ID = #' Set the value to be used by the following `INSERT' command when inserting an `AUTO_INCREMENT' value. This is mainly used with the update log. __set__ use constant H_GRANT => <<'__grant__'; GRANT priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} TO user_name [IDENTIFIED BY 'password'] [, user_name [IDENTIFIED BY 'password'] ...] [WITH GRANT OPTION] REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} FROM user_name [, user_name ...] `GRANT' is implemented in *MySQL* 3.22.11 or later. For earlier *MySQL* versions, the `GRANT' statement does nothing. The `GRANT' and `REVOKE' commands allow system administrators to grant and revoke rights to *MySQL* users at four privilege levels: *Global level* Global privileges apply to all databases on a given server. These privileges are stored in the `mysql.user' table. *Database level* Database privileges apply to all tables in a given database. These privileges are stored in the `mysql.db' and `mysql.host' tables. *Table level* Table privileges apply to all columns in a given table. These privileges are stored in the `mysql.tables_priv' table. *Column level* Column privileges apply to single columns in a given table. These privileges are stored in the `mysql.columns_priv' table. For examples of how `GRANT' works, see *Note Adding users::. For the `GRANT' and `REVOKE' statements, `priv_type' may be specified as any of the following: ALL PRIVILEGES FILE RELOAD ALTER INDEX SELECT CREATE INSERT SHUTDOWN DELETE PROCESS UPDATE DROP REFERENCES USAGE `ALL' is a synonym for `ALL PRIVILEGES'. `REFERENCES' is not yet implemented. `USAGE' is currently a synonym for "no privileges". It can be used when you want to create a user that has no privileges. To revoke the *grant* privilege from a user, use a `priv_type' value of `GRANT OPTION': REVOKE GRANT OPTION ON ... FROM ...; The only `priv_type' values you can specify for a table are `SELECT', `INSERT', `UPDATE', `DELETE', `CREATE', `DROP', `GRANT', `INDEX' and `ALTER'. The only `priv_type' values you can specify for a column (that is, when you use a `column_list' clause) are `SELECT', `INSERT' and `UPDATE'. You can set global privileges by using `ON *.*' syntax. You can set database privileges by using `ON db_name.*' syntax. If you specify `ON *' and you have a current database, you will set the privileges for that database. (*Warning:* If you specify `ON *' and you _don't_ have a current database, you will affect the global privileges!) __grant__ use constant H_CREATE_INDEX => <<'__create_index__'; CREATE [UNIQUE] INDEX index_name ON tbl_name (col_name[(length)],... ) The `CREATE INDEX' statement doesn't do anything in *MySQL* prior to version 3.22. In 3.22 or later, `CREATE INDEX' is mapped to an `ALTER TABLE' statement to create indexes. *Note `ALTER TABLE': ALTER TABLE. Normally, you create all indexes on a table at the time the table itself is created with `CREATE TABLE'. *Note `CREATE TABLE': CREATE TABLE. `CREATE INDEX' allows you to add indexes to existing tables. A column list of the form `(col1,col2,...)' creates a multiple-column index. Index values are formed by concatenating the values of the given columns. For `CHAR' and `VARCHAR' columns, indexes can be created that use only part of a column, using `col_name(length)' syntax. (On `BLOB' and `TEXT' columns the length is required). The statement shown below creates an index using the first 10 characters of the `name' column: mysql> CREATE INDEX part_of_name ON customer (name(10)); __create_index__ use constant H_DROP_INDEX => <<'__drop_index__'; DROP INDEX index_name ON tbl_name `DROP INDEX' drops the index named `index_name' from the table `tbl_name'. `DROP INDEX' doesn't do anything in *MySQL* prior to version 3.22. In 3.22 or later, `DROP INDEX' is mapped to an `ALTER TABLE' statement to drop the index. *Note `ALTER TABLE': ALTER TABLE. __drop_index__ use constant H_COMMENTS => <<'__comments__'; The *MySQL* server supports the `# to end of line', `-- to end of line' and `/* in-line or multiple-line */' comment styles: mysql> select 1+1; # This comment continues to the end of line mysql> select 1+1; -- This comment continues to the end of line mysql> select 1 /* this is an in-line comment */ + 1; mysql> select 1+ /* this is a multiple-line comment */ 1; Note that the `--' comment style requires you to have at least one space after the `--'! Although the server understands the comment syntax just described, there are some limitations on the way that the `mysql' client parses `/* ... */' comments: * Single-quote and double-quote characters are taken to indicate the beginning of a quoted string, even within a comment. If the quote is not matched by a second quote within the comment, the parser doesn't realize the comment has ended. If you are running `mysql' interactively, you can tell that it has gotten confused like this because the prompt changes from `mysql>' to `'>' or `">'. * A semicolon is taken to indicate the end of the current SQL statement and anything following it to indicate the beginning of the next statement. These limitations apply both when you run `mysql' interactively and when you put commands in a file and tell `mysql' to read its input from that file with `mysql < some-file'. __comments__ use constant H_CREATE_FUNCTION => <<'__create_function__'; CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|REAL|INTEGER} SONAME shared_library_name DROP FUNCTION function_name A user-definable function (UDF) is a way to extend *MySQL* with a new function that works like native (built in) *MySQL* functions such as `ABS()' and `CONCAT()'. `AGGREGATE' is a new option for *MySQL* 3.23. An `AGGREGATE' function works exactly like a native *MySQL* `GROUP' function like `SUM' or `COUNT()'. `CREATE FUNCTION' saves the function's name, type and shared library name in the `mysql.func' system table. You must have the *insert* and *delete* privileges for the `mysql' database to create and drop functions. __create_function__ use constant H_RESERVED_WORDS => <<'__reserved_words__'; Is MySQL picky about reserved words? ==================================== A common problem stems from trying to create a table with column names that use the names of datatypes or functions built into *MySQL*, such as `TIMESTAMP' or `GROUP'. You're allowed to do it (for example, `ABS' is an allowed column name), but whitespace is not allowed between a function name and the `(' when using functions whose names are also column names. The following words are explicitly reserved in *MySQL*. Most of them are forbidden by ANSI SQL92 as column and/or table names (for example, `group'). A few are reserved because *MySQL* needs them and is (currently) using a `yacc' parser: `action' `add' `aggregate' `all' `alter' `after' `and' `as' `asc' `avg' `avg_row_length' `auto_increment' `between' `bigint' `bit' `binary' `blob' `bool' `both' `by' `cascade' `case' `char' `character' `change' `check' `checksum' `column' `columns' `comment' `constraint' `create' `cross' `current_date' `current_time' `current_timestamp' `data' `database' `databases' `date' `datetime' `day' `day_hour' `day_minute' `day_second' `dayofmonth' `dayofweek' `dayofyear' `dec' `decimal' `default' `delayed' `delay_key_write' `delete' `desc' `describe' `distinct' `distinctrow' `double' `drop' `end' `else' `escape' `escaped' `enclosed' `enum' `explain' `exists' `fields' `file' `first' `float' `float4' `float8' `flush' `foreign' `from' `for' `full' `function' `global' `grant' `grants' `group' `having' `heap' `high_priority' `hour' `hour_minute' `hour_second' `hosts' `identified' `ignore' `in' `index' `infile' `inner' `insert' `insert_id' `int' `integer' `interval' `int1' `int2' `int3' `int4' `int8' `into' `if' `is' `isam' `join' `key' `keys' `kill' `last_insert_id' `leading' `left' `length' `like' `lines' `limit' `load' `local' `lock' `logs' `long' `longblob' `longtext' `low_priority' `max' `max_rows' `match' `mediumblob' `mediumtext' `mediumint' `middleint' `min_rows' `minute' `minute_second' `modify' `month' `monthname' `myisam' `natural' `numeric' `no' `not' `null' `on' `optimize' `option' `optionally' `or' `order' `outer' `outfile' `pack_keys' `partial' `password' `precision' `primary' `procedure' `process' `processlist' `privileges' `read' `real' `references' `reload' `regexp' `rename' `replace' `restrict' `returns' `revoke' `rlike' `row' `rows' `second' `select' `set' `show' `shutdown' `smallint' `soname' `sql_big_tables' `sql_big_selects' `sql_low_priority_updates'`sql_log_off' `sql_log_update' `sql_select_limit' `sql_small_result' `sql_big_result' `sql_warnings' `straight_join' `starting' `status' `string' `table' `tables' `temporary' `terminated' `text' `then' `time' `timestamp' `tinyblob' `tinytext' `tinyint' `trailing' `to' `type' `use' `using' `unique' `unlock' `unsigned' `update' `usage' `values' `varchar' `variables' `varying' `varbinary' `with' `write' `when' `where' `year' `year_month' `zerofill' The following symbols (from the table above) are disallowed by ANSI SQL but allowed by *MySQL* as column/table names. This is because some of these names are very natural names and a lot of people have already used them. * `ACTION' * `BIT' * `DATE' * `ENUM' * `NO' * `TEXT' * `TIME' * `TIMESTAMP' __reserved_words__ %HELP = ( arithmetic => H_ARITHMETIC, bit_operators => H_BIT_OPERATORS, logical_operators => H_LOGICAL_OPERATORS, comparison => H_COMPARISON, isnull => H_ISNULL, coalesce => H_COALESCE, interval => H_INTERVAL, string_comparison => H_STRING_COMPARISON, strcmp => H_STRCMP, binary => H_BINARY, ifnull => H_IFNULL, nullif => H_NULLIF, if => H_IF, case => H_CASE, flow_control => H_FLOW_CONTROL, abs => H_ABS, sign => H_SIGN, mod => H_MOD, floor => H_FLOOR, ceiling => H_CEILING, round => H_ROUND, round => H_ROUND, exp => H_EXP, log => H_LOG, log10 => H_LOG10, pow => H_POW, sqrt => H_SQRT, pi => H_PI, cos => H_COS, sin => H_SIN, tan => H_TAN, acos => H_ACOS, asin => H_ASIN, atan => H_ATAN, atan2 => H_ATAN2, cot => H_COT, rand => H_RAND, least => H_LEAST, greatest => H_GREATEST, degrees => H_DEGREES, radians => H_RADIANS, truncate => H_TRUNCATE, numeric_functions => H_NUMERIC_FUNCTIONS, ascii => H_ASCII, ord => H_ORD, conv => H_CONV, bin => H_BIN, oct => H_OCT, hex => H_HEX, char => H_CHAR, concat => H_CONCAT, concat_ws => H_CONCAT_WS, length => H_LENGTH, octet_length => H_OCTET_LENGTH, char_length => H_CHAR_LENGTH, character_length => H_CHARACTER_LENGTH, locate => H_LOCATE, position => H_POSITION, instr => H_INSTR, lpad => H_LPAD, rpad => H_RPAD, left => H_LEFT, right => H_RIGHT, mid => H_MID, substring => H_SUBSTRING, substring_index => H_SUBSTRING_INDEX, ltrim => H_LTRIM, rtrim => H_RTRIM, trim => H_TRIM, soundex => H_SOUNDEX, space => H_SPACE, fn_replace => H_FN_REPLACE, repeat => H_REPEAT, reverse => H_REVERSE, fn_insert => H_FN_INSERT, elt => H_ELT, field => H_FIELD, find_in_set => H_FIND_IN_SET, make_set => H_MAKE_SET, export_set => H_EXPORT_SET, lcase => H_LCASE, lower => H_LOWER, ucase => H_UCASE, upper => H_UPPER, load_file => H_LOAD_FILE, string_functions => H_STRING_FUNCTIONS, dayofweek => H_DAYOFWEEK, weekday => H_WEEKDAY, dayofmonth => H_DAYOFMONTH, dayofyear => H_DAYOFYEAR, month => H_MONTH, dayname => H_DAYNAME, monthname => H_MONTHNAME, quarter => H_QUARTER, week => H_WEEK, year => H_YEAR, yearweek => H_YEARWEEK, hour => H_HOUR, minute => H_MINUTE, second => H_SECOND, period_add => H_PERIOD_ADD, period_diff => H_PERIOD_DIFF, date_add => H_DATE_ADD, to_days => H_TO_DAYS, from_days => H_FROM_DAYS, date_format => H_DATE_FORMAT, time_format => H_TIME_FORMAT, curdate => H_CURDATE, curtime => H_CURTIME, now => H_NOW, unix_timestamp => H_UNIX_TIMESTAMP, from_unixtime => H_FROM_UNIXTIME, sec_to_time => H_SEC_TO_TIME, time_to_sec => H_TIME_TO_SEC, date_time_functions => H_DATE_TIME_FUNCTIONS, database => H_DATABASE, user => H_USER, password => H_PASSWORD, encrypt => H_ENCRYPT, encode => H_ENCODE, decode => H_DECODE, md5 => H_MD5, last_insert_id => H_LAST_INSERT_ID, format => H_FORMAT, version => H_VERSION, connection_id => H_CONNECTION_ID, get_lock => H_GET_LOCK, release_lock => H_RELEASE_LOCK, benchmark => H_BENCHMARK, inet_ntoa => H_INET_NTOA, inet_aton => H_INET_ATON, misc_functions => H_MISC_FUNCTIONS, count => H_COUNT, avg => H_AVG, min => H_MIN, sum => H_SUM, std => H_STD, bit_or => H_BIT_OR, bit_and => H_BIT_AND, group_by_functions => H_GROUP_BY_FUNCTIONS, data_types => H_DATA_TYPES, mysql_variables => H_MYSQL_VARIABLES, create_database => H_CREATE_DATABASE, drop_database => H_DROP_DATABASE, alter_table => H_ALTER_TABLE, drop_table => H_DROP_TABLE, optimize_table => H_OPTIMIZE_TABLE, check_table => H_CHECK_TABLE, repair_table => H_REPAIR_TABLE, delete => H_DELETE, select => H_SELECT, join => H_JOIN, insert => H_INSERT, replace => H_REPLACE, load_data => H_LOAD_DATA, update => H_UPDATE, use => H_USE, flush => H_FLUSH, kill => H_KILL, show => H_SHOW, explain => H_EXPLAIN, describe => H_DESCRIBE, lock => H_LOCK, set => H_SET, grant => H_GRANT, create_index => H_CREATE_INDEX, drop_index => H_DROP_INDEX, comments => H_COMMENTS, create_function => H_CREATE_FUNCTION, reserved_words => H_RESERVED_WORDS, power => H_POW, date_sub => H_DATE_ADD, adddate => H_DATE_ADD, subdate => H_DATE_ADD, sysdate => H_NOW, system_user => H_USER, session_user => H_USER, max => H_MIN, stddev => H_STD ); sub help_map ($) { return \%HELP } __END__ perl -n -e 'if(/^\`(\w+)\((.*)\)\x27/){ $lim && print(STDOUT "__${lim}__\n\n"); print(STDOUT "use constant H_$1 => <<\x27__",lc($1),"__\x27;\n$1($2):\n\n"); $lim = lc($1) } else { print(STDOUT $_) } END { print(STDOUT "__${lim}__\n") }'
