mysql中sleep函数的时间为什么效果是翻倍的

mysql中sleep函数的时间为什么效果是翻倍的

mysql> select * from ff;
+------+
| id   |
+------+
|   12 |
|   13 |
+------+
2 rows in set (0.00 sec)

mysql> select sleep(1),id from ff;
+----------+------+
| sleep(1) | id   |
+----------+------+
|        0 |   12 |
|        0 |   13 |
+----------+------+
2 rows in set (2.00 sec)

mysql> select sleep(2),id from ff;
+----------+------+
| sleep(2) | id   |
+----------+------+
|        0 |   12 |
|        0 |   13 |
+----------+------+
2 rows in set (4.00 sec)