mysql中

问题描述:

今天在看mysql的时间函数,now()和sysdate(),记录下两者之间有什么不同.

实验过程:

mysql> select now(),sleep(2),now();
+---------------------+----------+---------------------+
| now()               | sleep(2) | now()               |
+---------------------+----------+---------------------+
| 2018-06-01 15:17:18 |        0 | 2018-06-01 15:17:18 |
+---------------------+----------+---------------------+
1 row in set (2.00 sec)

mysql> select sysdate(),sleep(2),sysdate();
+---------------------+----------+---------------------+
| sysdate()           | sleep(2) | sysdate()           |
+---------------------+----------+---------------------+
| 2018-06-01 15:17:34 |        0 | 2018-06-01 15:17:36 |
+---------------------+----------+---------------------+
1 row in set (2.00 sec)

mysql> select now(),sleep(2),now(),sleep(1),now(),now();
+---------------------+----------+---------------------+----------+---------------------+---------------------+
| now()               | sleep(2) | now()               | sleep(1) | now()               | now()               |
+---------------------+----------+---------------------+----------+---------------------+---------------------+
| 2018-06-01 15:21:29 |        0 | 2018-06-01 15:21:29 |        0 | 2018-06-01 15:21:29 | 2018-06-01 15:21:29 |
+---------------------+----------+---------------------+----------+---------------------+---------------------+
1 row in set (③00 sec)

mysql> select sysdate(),sleep(2),sysdate(),sleep(1),sysdate(),sysdate();
+---------------------+----------+---------------------+----------+---------------------+---------------------+
| sysdate()           | sleep(2) | sysdate()           | sleep(1) | sysdate()           | sysdate()           |
+---------------------+----------+---------------------+----------+---------------------+---------------------+
| 2018-06-01 15:21:52 |        0 | 2018-06-01 15:21:54 |        0 | 2018-06-01 15:21:55 | 2018-06-01 15:21:55 |
+---------------------+----------+---------------------+----------+---------------------+---------------------+
1 row in set (③00 sec)

小结:

now()返回的时间是SQL语句执行的时间,无论在一次SQL语句中now()函数被执行多少次.即SQL开始执行的时间.

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