下面我们举例介绍一下MySQL SQL Profiler的使用方法：

首先，开启 MySQL SQL Profiler

mysql> SELECT @@profiling;

+-------------+

| @@profiling |

+-------------+

| 0 |

+-------------+

1 row in set (0.00 sec)

mysql> SET profiling = 1;

Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@profiling;

+-------------+

| @@profiling |

+-------------+

| 1 |

+-------------+

1 row in set (0.00 sec)默认情况下 profiling 的值为 0 表示 MySQL SQL Profiler 处于 OFF 状态，开启 SQL 性能分析器后 profiling 的值为 1.

通过 sql 性能分析器，我们来对比一下 下列语句前后 2 次执行过程的差异，对我们了解 sql 的详细执行过程是非常有帮助的。

mysql> create table t_engines select * from t_engines1;

Query OK, 57344 rows affected (0.10 sec)

Records: 57344 Duplicates: 0 Warnings: 0

mysql> select count(*) from t_engines;

+----------+

| count(*) |

+----------+

| 57344 |

+----------+

1 row in set (0.00 sec)

mysql> select count(*) from t_engines;

+----------+

| count(*) |

+----------+

| 57344 |

+----------+

1 row in set (0.00 sec)

mysql> SHOW PROFILES;

+----------+------------+-------------------------------------------------+

| Query_ID | Duration | Query |

+----------+------------+-------------------------------------------------+

| 26 | 0.10213775 | create table t_engines select * from t_engines1 |

| 27 | 0.00032775 | select count(*) from t_engines |

| 28 | 0.00003850 | select count(*) from t_engines |

+----------+------------+-------------------------------------------------+

15 rows in set (0.01 sec)

mysql> SHOW PROFILE FOR QUERY 27;

+--------------------------------+------------+

| Status | Duration |

+--------------------------------+------------+