MySQL学习笔记八：日期/时间的处理

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, 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

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)<right('1990-07-30',5)) as age;
+------+
| age  |
+------+
|   24 |
+------+
1 row in set (0.05 sec)