MySQL日期时间的处理,在其官网文档上都有详细的阐述，想了解更多的同学可自行查阅。

1.查询当前日期时间：函数有now(),localtime(),current_timestamp(),sysdate()。

mysql> select now(),localtime(),current_timestamp(),sysdate();+---------------------+---------------------+---------------------+---------------------+| now()               | localtime()         | current_timestamp() | sysdate()           |+---------------------+---------------------+---------------------+---------------------+| 2015-04-16 09:29:18 | 2015-04-16 09:29:18 | 2015-04-16 09:29:18 | 2015-04-16 09:29:18 |+---------------------+---------------------+---------------------+---------------------+1 row in set (0.00 sec)

但是now()与sysdate()有点差异的，一个语句中now()的值是不变的，而sysdate()是动态获取的，例如

mysql> select now(),sleep(2),now();+---------------------+----------+---------------------+| now()               | sleep(2) | now()               |+---------------------+----------+---------------------+| 2015-04-16 09:34:30 |        0 | 2015-04-16 09:34:30 |+---------------------+----------+---------------------+1 row in set (2.00 sec)mysql> select sysdate(),sleep(2),sysdate();+---------------------+----------+---------------------+| sysdate()           | sleep(2) | sysdate()           |+---------------------+----------+---------------------+| 2015-04-16 09:35:15 |        0 | 2015-04-16 09:35:17 |+---------------------+----------+---------------------+1 row in set (2.00 sec)-----有此结果可以看出，一般在生成环境中最好使用now()，当然也可以使用sysdate-is-now参数改变sysdate()的行为和now()一样------

2.获取当前日期，curdate()=current_date()=current_date

mysql> select curdate(),current_date(),current_date;+------------+----------------+--------------+| curdate()  | current_date() | current_date |+------------+----------------+--------------+| 2015-04-16 | 2015-04-16     | 2015-04-16   |+------------+----------------+--------------+1 row in set (0.00 sec)

3.获取当前时间，curtime()=current_time()=current_time

mysql> select curtime(),current_time(),current_time;+-----------+----------------+--------------+| curtime() | current_time() | current_time |+-----------+----------------+--------------+| 09:42:17  | 09:42:17       | 09:42:17     |+-----------+----------------+--------------+1 row in set (0.00 sec)

4.获取UTC日期时间，utc_date(),utc_time(),utc_timestamp()，中国属于东八区，故+8小时即可

mysql> select utc_date(),utc_time(),utc_timestamp();+------------+------------+---------------------+| utc_date() | utc_time() | utc_timestamp()     |+------------+------------+---------------------+| 2015-04-16 | 01:55:23   | 2015-04-16 01:55:23 |+------------+------------+---------------------+1 row in set (0.00 sec)

5.获取年，月，日

mysql> select year(now()),month(now()),day(now());+-------------+--------------+------------+| year(now()) | month(now()) | day(now()) |+-------------+--------------+------------+|        2015 |            4 |         16 |+-------------+--------------+------------+1 row in set (0.00 sec)

6.获取当前星期几，几月，以英文返回，dayname(),monthname()

mysql> select dayname(curdate()),monthname(curdate());+--------------------+----------------------+| dayname(curdate()) | monthname(curdate()) |+--------------------+----------------------+| Thursday           | April                |+--------------------+----------------------+1 row in set (0.03 sec)

7.获取某个日期在周，月，年中的位置，dayofweek(),dayofmonth,dayofyear()，如要返回中文周几，可以在程序中进行逻辑

mysql> set @d=now();Query OK, 0 rows affected (0.03 sec)mysql> select dayofweek(@d),dayofmonth(@d),dayofyear(@d);+---------------+----------------+---------------+| dayofweek(@d) | dayofmonth(@d) | dayofyear(@d) |+---------------+----------------+---------------+|             5 |             16 |           106 |+---------------+----------------+---------------+1 row in set (0.03 sec)

8.获取一个月的最后一天，last_day()，利用它可以得到某个月有多少天

mysql> select last_day(@d),day(last_day(@d));+--------------+-------------------+| last_day(@d) | day(last_day(@d)) |+--------------+-------------------+| 2015-04-30   |                30 |+--------------+-------------------+1 row in set (0.00 sec)

9.获取某天位于一年中的第N周week(date,3)=weekofyear()，week()函数的第二个参数用来设定以星期几做为一周的开始

mysql> select week(@d,3),weekofyear(@d);+------------+----------------+| week(@d,3) | weekofyear(@d) |+------------+----------------+|         16 |             16 |+------------+----------------+1 row in set (0.00 sec)

10.获取两个日期或者两个时间的相差，datediff(),timediff()

mysql> select datediff(curdate(),'2015-02-15'),timediff(curtime(),'09:09:09')+----------------------------------+--------------------------------+| datediff(curdate(),'2015-02-15') | timediff(curtime(),'09:09:09') |+----------------------------------+--------------------------------+|                               60 | 01:21:20                       |+----------------------------------+--------------------------------+1 row in set (0.05 sec)

11.为日期加上或减去一个间隔，date_add(),date_sub()

mysql> select date_add(curdate(),interval 1 day),date_sub(curdate(),interval 1 day);+------------------------------------+------------------------------------+| date_add(curdate(),interval 1 day) | date_sub(curdate(),interval 1 day) |+------------------------------------+------------------------------------+| 2015-04-17                         | 2015-04-15                         |+------------------------------------+------------------------------------+1 row in set (0.03 sec)mysql> select date_add(@d,interval '01:15:09' hour_second),date_sub(@d,interval '01:15:09' hour_second);+----------------------------------------------+----------------------------------------------+| date_add(@d,interval '01:15:09' hour_second) | date_sub(@d,interval '01:15:09' hour_second) |+----------------------------------------------+----------------------------------------------+| 2015-04-16 11:21:42                          | 2015-04-16 08:51:24                          |+----------------------------------------------+----------------------------------------------+1 row in set (0.00 sec)

12.时间与秒的转换，time_to_sec(),sec_to_time()

mysql> select time_to_sec(@d),sec_to_time(12389);+-----------------+--------------------+| time_to_sec(@d) | sec_to_time(12389) |+-----------------+--------------------+|           36393 | 03:26:29           |+-----------------+--------------------+1 row in set (0.00 sec)

13.日期与天数的转换，to_days(),from_days()

mysql> select to_days(@d),from_days(1460000);+-------------+--------------------+| to_days(@d) | from_days(1460000) |+-------------+--------------------+|      736069 | 3997-05-06         |+-------------+--------------------+1 row in set (0.00 sec)

14.字符串转换为日期，str_to_date(date,format)

mysql> select str_to_date('09/09/20','%Y/%m/%d');+------------------------------------+| str_to_date('09/09/20','%Y/%m/%d') |+------------------------------------+| 2009-09-20                         |+------------------------------------+1 row in set (0.00 sec)mysql> select str_to_date('09.09.20','%Y.%m.%d');+------------------------------------+| str_to_date('09.09.20','%Y.%m.%d') |+------------------------------------+| 2009-09-20                         |+------------------------------------+1 row in set (0.00 sec)

format标志含义：

%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%u Week (00..53), where Monday is the first day of the week%V Week (01..53), where Sunday is the first day of the week; used with %X%v Week (01..53), where Monday is the first day of the week; 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, fourdigits; used with %v%Y Year, numeric, four digits%y Year, numeric (two digits)%% A literal “%” character%x x, for any “x” not listed above

15.日期格式化，date_format(str,format)

mysql> select date_format('09.09.20','%Y:%m:%d');+------------------------------------+| date_format('09.09.20','%Y:%m:%d') |+------------------------------------+| 2009:09:20                         |+------------------------------------+1 row in set (0.00 sec)

16.日期/时间拼凑，makedate(year,dayofyear),maketime(hour,minute,second)

mysql> select makedate(2015,200),maketime(13,20,15);+--------------------+--------------------+| makedate(2015,200) | maketime(13,20,15) |+--------------------+--------------------+| 2015-07-19         | 13:20:15           |+--------------------+--------------------+1 row in set (0.00 sec)

17.unix时间戳，时间戳转换等，unix_timestamp(date),timestamp(date)

mysql> select unix_timestamp(),unix_timestamp('2009-09-09'),timestamp(now());+------------------+------------------------------+---------------------+| unix_timestamp() | unix_timestamp('2009-09-09') | timestamp(now())    |+------------------+------------------------------+---------------------+|       1429153960 |                   1252425600 | 2015-04-16 11:12:40 |+------------------+------------------------------+---------------------+1 row in set (0.00 sec)

18.在应用中碰到需要比较日期时，比如获取某一天的数据，不能使用“=”等于号来比较，使用"<>"，比如

select * from users where regDate<'2009-10-23' and regDate>='2009-10-22' //如果使用regDate='2009-10-22'相当于00:00:00

19.知道用户的生日得到年龄

mysql> select year(curdate())-year('1990-07-30')-(right(curdate(),5)