常见日期处理函数
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NOW([fsp])返回当前的日期和时间，格式为：'YYYY-MM-DD HH:MM:SS' 或 'YYYYMMDDHHMMSS'。具体使用哪种格式取决于NOW()函数使用的环境（字符串/数字）。mysql> SELECT NOW(); +---------------------+ | NOW() | +---------------------+ | 2019-03-28 06:46:39 | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT NOW() + 0; +----------------+ | NOW() + 0 | +----------------+ | 20190328064659 | +----------------+ 1 row in set (0.00 sec)还可以在函数中提供一个fsp参数（0-6）来指定秒数的精度：
mysql> SELECT NOW(6); +----------------------------+ | NOW(6) | +----------------------------+ | 2019-03-28 06:47:11.620058 | +----------------------------+ 1 row in set (0.00 sec)NOW()和SYSDATE()都可以返回当前时间，二者的区别在于，NOW()返回的时包含该函数的语句开始运行的时间，而SYSDATE()返回的是函数执行的时间。另一个区别是，在执行SET TIMESTAMP语句后，SYSDATE()的返回值不受影响，而NOW()则会返回设定的值。 -
CURDATE()返回当前的日期，格式为：'YYYY-MM-DD' 或 'YYYYMMDD'。具体使用哪种格式取决于该函数使用的环境（字符串/数字）。mysql> SELECT CURDATE(); +------------+ | CURDATE() | +------------+ | 2019-03-28 | +------------+ 1 row in set (0.01 sec) mysql> SELECT CURDATE() + 0; +---------------+ | CURDATE() + 0 | +---------------+ | 20190328 | +---------------+ 1 row in set (0.00 sec) -
CURTIME([fsp])返回当前的时间，格式为：'HH:MM:SS' 或 'HHMMSS'。具体使用哪种格式取决于该函数使用的环境（字符串/数字）。还可以在函数中提供一个fsp参数（0-6）来指定秒数的精度：mysql> SELECT CURTIME(); +-----------+ | CURTIME() | +-----------+ | 07:03:54 | +-----------+ 1 row in set (0.00 sec) mysql> SELECT CURTIME() + 0; +---------------+ | CURTIME() + 0 | +---------------+ | 70404 | +---------------+ 1 row in set (0.00 sec) mysql> SELECT CURTIME(6) + 0; +----------------+ | CURTIME(6) + 0 | +----------------+ | 70416.578713 | +----------------+ 1 row in set (0.00 sec) -
DATE(expr)提取日期表达式/日期时间表达式中的日期部分。mysql> SELECT DATE('2010-10-05 09:29:45'); +-----------------------------+ | DATE('2010-10-05 09:29:45') | +-----------------------------+ | 2010-10-05 | +-----------------------------+ 1 row in set (0.00 sec) -
EXTRACT(unit FROM date)从日期表达式/日期时间表达式中提取给定的unit。mysql> SELECT EXTRACT(YEAR FROM '2008-09-12'); +---------------------------------+ | EXTRACT(YEAR FROM '2008-09-12') | +---------------------------------+ | 2008 | +---------------------------------+ 1 row in set (0.02 sec) mysql> SELECT EXTRACT(QUARTER FROM '2008-09-12'); +------------------------------------+ | EXTRACT(QUARTER FROM '2008-09-12') | +------------------------------------+ | 3 | +------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT EXTRACT(YEAR_MONTH FROM '2008-09-12'); +---------------------------------------+ | EXTRACT(YEAR_MONTH FROM '2008-09-12') | +---------------------------------------+ | 200809 | +---------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT EXTRACT(HOUR_MICROSECOND FROM '2008-09-12 12:23:55.023111'); +-------------------------------------------------------------+ | EXTRACT(HOUR_MICROSECOND FROM '2008-09-12 12:23:55.023111') | +-------------------------------------------------------------+ | 122355023111 | +-------------------------------------------------------------+ 1 row in set (0.00 sec)常见的unit值和其对应的格式如下表：
unit Value Expected expr Format MICROSECONDMICROSECONDSSECONDSECONDSMINUTEMINUTESHOURHOURSDAYDAYSWEEKWEEKSMONTHMONTHSQUARTERQUARTERSYEARYEARSSECOND_MICROSECOND'SECONDS.MICROSECONDS'MINUTE_MICROSECOND'MINUTES:SECONDS.MICROSECONDS'MINUTE_SECOND'MINUTES:SECONDS'HOUR_MICROSECOND'HOURS:MINUTES:SECONDS.MICROSECONDS'HOUR_SECOND'HOURS:MINUTES:SECONDS'HOUR_MINUTE'HOURS:MINUTES'DAY_MICROSECOND'DAYS HOURS:MINUTES:SECONDS.MICROSECONDS'DAY_SECOND'DAYS HOURS:MINUTES:SECONDS'DAY_MINUTE'DAYS HOURS:MINUTES'DAY_HOUR'DAYS HOURS'YEAR_MONTH'YEARS-MONTHS' -
DATE_ADD(date,INTERVAL expr unit), DATE_SUB(date,INTERVAL expr unit)这两个函数可以对日期进行数学计算。date参数指定了起始的日期/日期时间值expr参数指定了需要在起始日期的基础上增加/减少的时间区间。expr被视为一个字符串，可以以'-'开始去表示一个负的间隔。unit表示expr的格式，标明了expr该以何种方式进行翻译返回值可能为：
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DATE：当date参数为一个日期表达式，并且计算过程中只涉及了DATE, MONTH, DAY。 -
DATETIME：当date参数为一个日期时间表达式/时间戳，或者unit值使用了HOURS, MINUTES, SECONDS。 - 除了1，2以外的其他情况均返回字符串。
mysql> SELECT DATE_ADD('2009-03-11', INTERVAL 1 DAY); +----------------------------------------+ | DATE_ADD('2009-03-11', INTERVAL 1 DAY) | +----------------------------------------+ | 2009-03-12 | +----------------------------------------+ 1 row in set (0.01 sec) mysql> SELECT DATE_SUB('2009-03-12', INTERVAL 1 YEAR); +-----------------------------------------+ | DATE_SUB('2009-03-12', INTERVAL 1 YEAR) | +-----------------------------------------+ | 2008-03-12 | +-----------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT DATE_ADD('2009-04-10 19:34:12', INTERVAL '25:48' MINUTE_SECOND); +-----------------------------------------------------------------+ | DATE_ADD('2009-04-10 19:34:12', INTERVAL '25:48' MINUTE_SECOND) | +-----------------------------------------------------------------+ | 2009-04-10 20:00:00 | +-----------------------------------------------------------------+ 1 row in set (0.00 sec) -
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DATEDIFF(expr1,expr2)返回expr1-expr2日期的差值(DAY)，expr1和expr2可以是日期表达式/日期时间表达式，但是只有日期部分会参与运算。mysql> SELECT DATEDIFF('2009-01-01','2008-01-01'); +-------------------------------------+ | DATEDIFF('2009-01-01','2008-01-01') | +-------------------------------------+ | 366 | +-------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT DATEDIFF('2010-10-01 20:12:34','2010-09-30 12:34:22'); +-------------------------------------------------------+ | DATEDIFF('2010-10-01 20:12:34','2010-09-30 12:34:22') | +-------------------------------------------------------+ | 1 | +-------------------------------------------------------+ 1 row in set (0.01 sec) -
DATE_FORMAT(date, format)根据format指定的格式返回日期。format是一个我们指定的模版，我们通过使用区分符来指定我们想要的某种特殊格式。mysql> SELECT DATE_FORMAT('2000-10-01','%b,%D,%Y'); +--------------------------------------+ | DATE_FORMAT('2000-10-01','%b,%D,%Y') | +--------------------------------------+ | Oct,1st,2000 | +--------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT DATE_FORMAT('2010-08-27','day of the week: %w'); +-------------------------------------------------+ | DATE_FORMAT('2010-08-27','day of the week: %w') | +-------------------------------------------------+ | day of the week: 5 | +-------------------------------------------------+ 1 row in set (0.00 sec)
format是一个包含有区分符(specifier)的字符串，常用的区分符有：
| Specifier | Description |
|---|---|
%a |
Abbreviated weekday name (Sun..Sat) |
%b |
Abbreviated month name (Jan..Dec) |
%c |
Month, numeric (0..12) |
%D |
Day of the month with English suffix (0th, 1st, 2nd, 3rd, …) |
%d |
Day of the month, numeric (00..31) |
%e |
Day of the month, numeric (0..31) |
%f |
Microseconds (000000..999999) |
%H |
Hour (00..23) |
%h |
Hour (01..12) |
%I |
Hour (01..12) |
%i |
Minutes, numeric (00..59) |
%j |
Day of year (001..366) |
%k |
Hour (0..23) |
%l |
Hour (1..12) |
%M |
Month name (January..December) |
%m |
Month, numeric (00..12) |
%p |
AM or PM |
%r |
Time, 12-hour (hh:mm:ss followed by AM or PM) |
%S |
Seconds (00..59) |
%s |
Seconds (00..59) |
%T |
Time, 24-hour (hh:mm:ss) |
%U |
Week (00..53), where Sunday is the first day of the week; WEEK() mode 0 |
%u |
Week (00..53), where Monday is the first day of the week; WEEK() mode 1 |
%V |
Week (01..53), where Sunday is the first day of the week; WEEK() mode 2; used with %X |
%v |
Week (01..53), where Monday is the first day of the week; WEEK() mode 3; used with %x |
%W |
Weekday name (Sunday..Saturday) |
%w |
Day of the week (0=Sunday..6=Saturday) |
%X |
Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V |
%x |
Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v |
%Y |
Year, numeric, four digits |
%y |
Year, numeric (two digits) |
%% |
A literal % character |
%*x* |
x, for any “x” not listed above |
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ADDDATE(date,INTERVAL expr unit), ADDDATE(expr, days)当使用
INTERVAL作为第二个参数时，ADDDATE()与DATE_ADD()的用法是相同的。当使用
days作为第二个参数时，MySQL会把days当作一个整数的天数添加到expr。mysql> SELECT ADDDATE('2011-10-01', 20); +---------------------------+ | ADDDATE('2011-10-01', 20) | +---------------------------+ | 2011-10-21 | +---------------------------+ 1 row in set (0.00 sec) -
ADDTIME(expr1, expr2)expr1是一个时间表达式/日期时间表达式expr2是一个时间表达式ADDTIME()会在expr1的基础上加上expr2，并返回结果mysql> SELECT ADDTIME('2001-01-01 16:19:29', '00:10:01.1111'); +-------------------------------------------------+ | ADDTIME('2001-01-01 16:19:29', '00:10:01.1111') | +-------------------------------------------------+ | 2001-01-01 16:29:30.111100 | +-------------------------------------------------+ 1 row in set (0.00 sec) -
DAY(date)是DAYOFMONTH()的同义词，返回date中的日期是该月的哪一天，范围1～31。mysql> SELECT DAY('2018-04-12 18:45:26'); +----------------------------+ | DAY('2018-04-12 18:45:26') | +----------------------------+ | 12 | +----------------------------+ 1 row in set (0.00 sec) -
YEAR()返回日期所在的年份，范围1000～9999。mysql> SELECT YEAR('1999-03-04'); +--------------------+ | YEAR('1999-03-04') | +--------------------+ | 1999 | +--------------------+ 1 row in set (0.00 sec)
常用的文本处理函数
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LEFT(str,len)返回str字符串中最左侧的len个字符，如果参数为NULL则返回NULL。mysql> SELECT LEFT('lifetime',4); +--------------------+ | LEFT('lifetime',4) | +--------------------+ | life | +--------------------+ 1 row in set (0.01 sec) -
RIGHT(str,len)返回str字符串中最右侧的len个字符，如果参数为NULL则返回NULL。mysql> SELECT RIGHT('lifetime',4); +---------------------+ | RIGHT('lifetime',4) | +---------------------+ | time | +---------------------+ 1 row in set (0.00 sec) -
LENGTH(str)返回str字符串的长度，以字节计算，一个多字节字符会按照多个字节计算长度。而当使用CHAR_LENGTH()时，会将一个多字节字符以一个字节计算长度，即长度为1。mysql> SELECT LENGTH('lifetime'); +--------------------+ | LENGTH('lifetime') | +--------------------+ | 8 | +--------------------+ 1 row in set (0.00 sec) mysql> SELECT LENGTH('生活'); +------------------+ | LENGTH('生活') | +------------------+ | 6 | +------------------+ 1 row in set (0.00 sec) mysql> SELECT CHAR_LENGTH('生活'); +-----------------------+ | CHAR_LENGTH('生活') | +-----------------------+ | 2 | +-----------------------+ 1 row in set (0.00 sec) -
LOWER(str)根据目前的字符集将str中的所有字符转换为小写并返回。mysql> SELECT LOWER('HELLO'); +----------------+ | LOWER('HELLO') | +----------------+ | hello | +----------------+ 1 row in set (0.00 sec) -
UPPER(str)根据目前的字符集将str中的所有字符转换为大写并返回。mysql> SELECT UPPER('hello'); +----------------+ | UPPER('hello') | +----------------+ | HELLO | +----------------+ 1 row in set (0.00 sec)注意：
LOWER()和UPPER()对二进制字符串无效（BINARY,VARBINARY,BLOB）。转换大小写时需要将其转换为非二进制字符串。 -
LTRIM(str)将str开头处的空格移除，返回移除空格后的字符串。该函数可以用于包含多字节字符的字符串。mysql> SELECT LTRIM(' shop'); +-------------------+ | LTRIM(' shop') | +-------------------+ | shop | +-------------------+ 1 row in set (0.00 sec) mysql> SELECT LTRIM(' 商店'); +---------------------+ | LTRIM(' 商店') | +---------------------+ | 商店 | +---------------------+ 1 row in set (0.00 sec) -
RTRIM(str)将`str尾部的空格移除，返回移除空格后的字符串。该函数可以用于包含多字节字符的字符串。mysql> SELECT LTRIM('shop '); +-------------------+ | LTRIM('shop ') | +-------------------+ | shop | +-------------------+ 1 row in set (0.00 sec) mysql> SELECT LTRIM('商店 '); +---------------------+ | LTRIM('商店 ') | +---------------------+ | 商店 | +---------------------+ 1 row in set (0.00 sec) -
TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str),TRIM([remstr FROM] str)将
str中所有的remstr前缀/后缀移除。如果没有使用BOTH,LEADING,TRAILING这些区分符，会假定使用BOTH。remstr是可选的，如果没有指定，则会移除空格。mysql> SELECT TRIM(' test '); +---------------------+ | TRIM(' test ') | +---------------------+ | test | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT TRIM(LEADING '-' FROM '---author---'); +---------------------------------------+ | TRIM(LEADING '-' FROM '---author---') | +---------------------------------------+ | author--- | +---------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT TRIM(TRAILING '-' FROM '---author---'); +----------------------------------------+ | TRIM(TRAILING '-' FROM '---author---') | +----------------------------------------+ | ---author | +----------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT TRIM(BOTH '-' FROM '---author---'); +------------------------------------+ | TRIM(BOTH '-' FROM '---author---') | +------------------------------------+ | author | +------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT TRIM('-' FROM '---author---'); +-------------------------------+ | TRIM('-' FROM '---author---') | +-------------------------------+ | author | +-------------------------------+ 1 row in set (0.00 sec) -
SUBSTRING(str, pos),SUBSTRING(str FROM pos),SUBSTRING(str,pos,len),SUBSTRING(str FROM pos FOR len)返回截取后的字符串。- 参数列表中没有
len参数时，会返回一个从pos位置开始的字符串。 - 参数列表中有
len参数时，会返回一个从pos位置开始，长度为len的字符串。 - 使用
FROM的是标准写法。 - 当
pos值为负数时，表示该位置是从字符串尾部开始计算的。 - 当
len小于1时，返回一个空的字符串
mysql> SELECT SUBSTRING('www.google.com', 5); +--------------------------------+ | SUBSTRING('www.google.com', 5) | +--------------------------------+ | google.com | +--------------------------------+ 1 row in set (0.01 sec) mysql> SELECT SUBSTRING('www.google.com' FROM 5); +------------------------------------+ | SUBSTRING('www.google.com' FROM 5) | +------------------------------------+ | google.com | +------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT SUBSTRING('www.google.com',5,6); +---------------------------------+ | SUBSTRING('www.google.com',5,6) | +---------------------------------+ | google | +---------------------------------+ 1 row in set (0.00 sec) mysql> SELECT SUBSTRING('www.google.com'FROM 5 FOR 6); +-----------------------------------------+ | SUBSTRING('www.google.com'FROM 5 FOR 6) | +-----------------------------------------+ | google | +-----------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT SUBSTRING('www.google.com',-3,3); +----------------------------------+ | SUBSTRING('www.google.com',-3,3) | +----------------------------------+ | com | +----------------------------------+ 1 row in set (0.00 sec) - 参数列表中没有