1、date函数简介：
MySQL数据库Date()日期函数，用于MySQL数据库查询当前日期，时间。
2、用法：
获取当前时间：
MySQL> select current_timestamp();
+---------------------+
| current_timestamp() |
+---------------------+
| 2010-01-18 21:24:37 |
+---------------------+
1 row in set (0.00 sec)
MySQL> select current_date();
+----------------+
| current_date() |
+----------------+
| 2010-01-18 |
+----------------+
1 row in set (0.00 sec)
MySQL> select current_time();
+----------------+
| current_time() |
+----------------+
| 21:24:46 |
+----------------+
1 row in set (0.00 sec)
Unix时间：
MySQL> select unix_timestamp();
+------------------+
| unix_timestamp() |
+------------------+
| 1263821184 |
+------------------+
1 row in set (0.00 sec)
MySQL> select from_unixtime(1263821182);
+---------------------------+
| from_unixtime(1263821182) |
+---------------------------+
| 2010-01-18 21:26:22 |
+---------------------------+
1 row in set (0.00 sec)
时间前后：
MySQL> select date_add(current_timestamp, interval 1 day);
+---------------------------------------------+
| date_add(current_timestamp, interval 1 day) |
+---------------------------------------------+
| 2010-01-19 21:27:53 |
+---------------------------------------------+
1 row in set (0.00 sec)
MySQL> select date_add(current_time, interval 1 day);
+----------------------------------------+
| date_add(current_time, interval 1 day) |
+----------------------------------------+
| NULL |
+----------------------------------------+
1 row in set, 1 warning (0.00 sec)
MySQL> select date_add(current_date, interval 1 day);
+----------------------------------------+
| date_add(current_date, interval 1 day) |
+----------------------------------------+
| 2010-01-19 |
+----------------------------------------+
1 row in set (0.00 sec)
MySQL> select date_sub(current_timestamp, interval 1 day);
+---------------------------------------------+
| date_sub(current_timestamp, interval 1 day) |
+---------------------------------------------+
| 2010-01-17 21:28:41 |
+---------------------------------------------+
1 row in set (0.00 sec)
MySQL> select date_sub(current_date, interval 1 day);
+----------------------------------------+
| date_sub(current_date, interval 1 day) |
+----------------------------------------+
| 2010-01-17 |
+----------------------------------------+
1 row in set (0.00 sec)
MySQL> select date_sub(current_time, interval 1 day);
+----------------------------------------+
| date_sub(current_time, interval 1 day) |
+----------------------------------------+
| NULL |
+----------------------------------------+
1 row in set, 1 warning (0.00 sec)
时间间隔：
MySQL> select datediff('2010-01-18','2010-01-17');
+-------------------------------------+
| datediff('2010-01-18','2010-01-17') |
+-------------------------------------+
| 1 |
+-------------------------------------+
1 row in set (0.00 sec)
MySQL> select timediff('2010-01-18 12:00','2010-01-17 11:00');
+-------------------------------------------------+
| timediff('2010-01-18 12:00','2010-01-17 11:00') |
+-------------------------------------------------+
| 25:00:00 |
+-------------------------------------------------+
1 row in set (0.00 sec)
时间转换：
MySQL> select time_to_sec('25:00:00');
+-------------------------+
| time_to_sec('25:00:00') |
+-------------------------+
| 90000 |
+-------------------------+
1 row in set (0.00 sec)
MySQL> select sec_to_time(90000);
+--------------------+
| sec_to_time(90000) |
+--------------------+
| 25:00:00 |
+--------------------+
1 row in set (0.00 sec)
