mysql sleep
mysql sleep
今天看到了一个sql:
select count(*), sleep(5) from test
第一次看到这个sleep函数,所以专门研究了一波。这个函数的语法是:SLEEP(duration)
, 其中duration的单位是秒
Sleeps (pauses) for the number of seconds given by the duration argument, then returns 0. The duration may have a fractional part. If the argument is NULL or negative, SLEEP() produces a warning, or an error in strict SQL mode.
When sleep returns normally (without interruption), it returns 0:
简单的说他可以让sql在执行的时候sleep一段时间。
mysql> SELECT SLEEP(1000);
+-------------+
| SLEEP(1000) |
+-------------+
| 0 |
+-------------+
When SLEEP() is the only thing invoked by a query that is interrupted, it returns 1 and the query itself returns no error. This is true whether the query is killed or times out:
- This statement is interrupted using KILL QUERY from another session:
mysql> SELECT SLEEP(1000);
+-------------+
| SLEEP(1000) |
+-------------+
| 1 |
+-------------+
- This statement is interrupted by timing out:
mysql> SELECT /*+ MAX_EXECUTION_TIME(1) */ SLEEP(1000);
+-------------+
| SLEEP(1000) |
+-------------+
| 1 |
+-------------+
这里解释一下上面的语法,那个语法是Mysql Optimizer Hints
When SLEEP() is only part of a query that is interrupted, the query returns an error:
- This statement is interrupted using KILL QUERY from another session:
mysql> SELECT 1 FROM t1 WHERE SLEEP(1000);
ERROR 1317 (70100): Query execution was interrupted
- This statement is interrupted by timing out:
mysql> SELECT /*+ MAX_EXECUTION_TIME(1000) */ 1 FROM t1 WHERE SLEEP(1000);
ERROR 3024 (HY000): Query execution was interrupted, maximum statement
execution time exceeded
This function is unsafe for statement-based replication. A warning is logged if you use this function when binlog_format is set to STATEMENT.