檢查mysql語句運轉時光的2種辦法

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網站運轉很慢的時刻，我就特殊起曉得為何這麼慢，所以我查啊查,數據庫相對是很主要的一部門，外面運轉的sql是相對不克不及放過的。日常平凡做項目標時刻，我也會留意sql語句的書寫，寫出一些高效的sql來，所以我會常常測試本身寫的sql語句。我把我曉得的二個辦法，總結一下收回來。

一，show profiles 之類的語句來檢查

1，查一下profile是否是翻開了，默許是不翻開的。

mysql> show profiles; 
Empty set (0.02 sec) 
mysql> show variables like "%pro%"; 
+---------------------------+-------+ 
| Variable_name | Value | 
+---------------------------+-------+ 
| profiling | OFF | 
| profiling_history_size | 15 | 
| protocol_version | 10 | 
| slave_compressed_protocol | OFF | 
+---------------------------+-------+ 
4 rows in set (0.00 sec)

我檢查一下profiles外面沒有器械，所以公司的電腦外面profile是沒有翻開的，我檢查了一下mysql變量，果真是OFF的。

2，開啟profile，然後測試

開啟profile

mysql> set profiling=1; 
Query OK, 0 rows affected (0.00 sec)

測試以下：

mysql> show tables; 
+----------------+ 
| Tables_in_test | 
+----------------+ 
| aa | 
| bb | 
| comment | 
| string_test | 
| user | 
+----------------+ 
5 rows in set (0.00 sec) 
mysql> select * from aa; 
+----+------+------------+------+ 
| id | name | nname | sex | 
+----+------+------------+------+ 
| 2 | tank | bbbb,4bbbb | NULL | 
| 3 | zhang| 3,c,u | NULL | 
+----+------+------------+------+ 
2 rows in set (0.00 sec) 
mysql> update aa set name='d'; 
Query OK, 2 rows affected (0.00 sec) 
Rows matched: 2 Changed: 2 Warnings: 0 
mysql> delete from bb; 
Query OK, 2 rows affected (0.00 sec) 
mysql> show profiles; 
+----------+------------+------------------------+ 
| Query_ID | Duration | Query | 
+----------+------------+------------------------+ 
| 1 | 0.00054775 | show tables | 
| 2 | 0.00022400 | select * from aa | 
| 3 | 0.00026275 | update aa set name='d' | 
| 4 | 0.00043000 | delete from bb | 
+----------+------------+------------------------+ 
4 rows in set (0.00 sec) 
mysql> show profile; 
+----------------------+-----------+ 
| Status | Duration | 
+----------------------+-----------+ 
| (initialization) | 0.0000247 | 
| checking permissions | 0.0000077 | 
| Opening tables | 0.0000099 | 
| System lock | 0.000004 | 
| Table lock | 0.000005 | 
| init | 0.0003057 | 
| query end | 0.0000062 | 
| freeing items | 0.000057 | 
| closing tables | 0.000008 | 
| logging slow query | 0.0000015 | 
+----------------------+-----------+ 
10 rows in set (0.00 sec) 
mysql> show profile for query 1; 
+----------------------+-----------+ 
| Status | Duration | 
+----------------------+-----------+ 
| (initialization) | 0.000028 | 
| checking permissions | 0.000007 | 
| Opening tables | 0.0000939 | 
| System lock | 0.0000017 | 
| Table lock | 0.0000055 | 
| init | 0.000009 | 
| optimizing | 0.0000027 | 
| statistics | 0.0000085 | 
| preparing | 0.0000065 | 
| executing | 0.000004 | 
| checking permissions | 0.000258 | 
| Sending data | 0.000049 | 
| end | 0.0000037 | 
| query end | 0.0000027 | 
| freeing items | 0.0000307 | 
| closing tables | 0.0000032 | 
| removing tmp table | 0.0000275 | 
| closing tables | 0.0000037 | 
| logging slow query | 0.000002 | 
+----------------------+-----------+ 
19 rows in set (0.00 sec) 
mysql> show profile for query 3; 
+----------------------+-----------+ 
| Status | Duration | 
+----------------------+-----------+ 
| (initialization) | 0.0000475 | 
| checking permissions | 0.0000077 | 
| Opening tables | 0.000026 | 
| System lock | 0.0000042 | 
| Table lock | 0.0000045 | 
| init | 0.0000205 | 
| Updating | 0.0000787 | 
| end | 0.0000567 | 
| query end | 0.000004 | 
| freeing items | 0.0000067 | 
| closing tables | 0.000004 | 
| logging slow query | 0.000002 | 
+----------------------+-----------+ 
12 rows in set (0.00 sec)

二，timestampdiff來檢查測試時光

mysql> set @d=now(); 
Query OK, 0 rows affected (0.00 sec) 
mysql> select * from comment; 
+------+-----+------+------------+---------------------+ 
| c_id | mid | name | content | datetime | 
+------+-----+------+------------+---------------------+ 
| 1 | 1 | ?? | 2222222211 | 2010-05-12 00:00:00 | 
| 2 | 1 | ?? | ????(??) | 2010-05-13 00:00:00 | 
| 3 | 2 | tank | ?????? | 0000-00-00 00:00:00 | 
+------+-----+------+------------+---------------------+ 
3 rows in set (0.00 sec) 
mysql> select timestampdiff(second,@d,now()); 
+--------------------------------+ 
| timestampdiff(second,@d,now()) | 
+--------------------------------+ 
| 0 | 
+--------------------------------+ 
1 row in set (0.00 sec) 

這類辦法有一點要留意，就是三條sql語句要盡可能連一路履行，否則誤差太年夜，基本禁絕

set @d=now(); 
select * from comment; 
select timestampdiff(second,@d,now()); 

假如是用敕令行來履行的話，有一點要留意，就是在select timestampdiff(second,@d,now());前面，必定要多copy一個空行，否則最初一個sql要你本身按回車履行，如許就禁絕了。

其實我認為吧，真正要我們關懷的是那些查詢慢的sql,由於真正影響速度的是他們，關於慢查詢的器械，有空寫一下。