日期时间函数

mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2016-06-26 18:39:55 |
+---------------------+
1 row in set (0.17 sec)

mysql> select curdate();
+------------+
| curdate()  |
+------------+
| 2016-06-26 |
+------------+
1 row in set (0.00 sec)

mysql> select curtime();
+-----------+
| curtime() |
+-----------+
| 18:40:14  |
+-----------+
1 row in set (0.00 sec)

mysql> select extract(day from "2012-4-5");
+------------------------------+
| extract(day from "2012-4-5") |
+------------------------------+
|                            5 |
+------------------------------+
1 row in set (0.18 sec)

mysql> select extract(year from "2012-4-5");   
+-------------------------------+
| extract(year from "2012-4-5") |
+-------------------------------+
|                          2012 |
+-------------------------------+
1 row in set (0.00 sec)

mysql> select extract(month from "2012-4-5");     
+--------------------------------+
| extract(month from "2012-4-5") |
+--------------------------------+
|                              4 |
+--------------------------------+
1 row in set (0.00 sec)

mysql> select sysdate();
+---------------------+
| sysdate() |
+---------------------+
| 2016-06-26 18:49:15 |
+---------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 month); 
+---------------------------------------+
| date_add("2012-4-5",interval 1 month) |
+---------------------------------------+
| 2012-05-05                            |
+---------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 year);
+--------------------------------------+
| date_add("2012-4-5",interval 1 year) |
+--------------------------------------+
| 2013-04-05                           |
+--------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 day);
+-------------------------------------+
| date_add("2012-4-5",interval 1 day) |
+-------------------------------------+
| 2012-04-06                          |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 minute);
+----------------------------------------+
| date_add("2012-4-5",interval 1 minute) |
+----------------------------------------+
| 2012-04-05 00:01:00                    |
+----------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 hour);
+--------------------------------------+
| date_add("2012-4-5",interval 1 hour) |
+--------------------------------------+
| 2012-04-05 01:00:00                  |
+--------------------------------------+
1 row in set (0.00 sec)

mysql> select date_add("2012-4-5",interval 1 second);
+----------------------------------------+
| date_add("2012-4-5",interval 1 second) |
+----------------------------------------+
| 2012-04-05 00:00:01 |
+----------------------------------------+
1 row in set (0.00 sec)

mysql> select datediff("2010-7-21","2010-7-28");
+-----------------------------------+
| datediff("2010-7-21","2010-7-28") |
+-----------------------------------+
|                                -7 |
+-----------------------------------+
1 row in set (0.01 sec)