【MySQL】日期、时间相关

参考：MySQL：日期函数、时间函数总结

now()

获得当前日期+时间（date + time）

select now();
+---------------------+
| now()               |
+---------------------+
| 2019-10-29 17:02:59 |
+---------------------+
1 row in set (0.00 sec)

sysdate()

获得当前日期+时间（date + time），与now()不同之处如下：

mysql> select sysdate(), sleep(3), sysdate();
+---------------------+----------+---------------------+
| sysdate()           | sleep(3) | sysdate()           |
+---------------------+----------+---------------------+
| 2019-10-29 17:05:19 |        0 | 2019-10-29 17:05:22 |
+---------------------+----------+---------------------+
1 row in set (3.07 sec)

mysql> select now(), sleep(3), now();
+---------------------+----------+---------------------+
| now()               | sleep(3) | now()               |
+---------------------+----------+---------------------+
| 2019-10-29 17:05:37 |        0 | 2019-10-29 17:05:37 |
+---------------------+----------+---------------------+
1 row in set (3.06 sec)

TO_DAYS(date)

给定日期，返回对应天数(年为0以来的天数)。

mysql> select TO_DAYS(20101029);
+-------------------+
| TO_DAYS(20101029) |
+-------------------+
|            734439 |
+-------------------+
1 row in set (0.01 sec)