mysql SQL分析常用工具

1、執行計劃

      運行執行計劃 可以很明顯知道SQL有無走索引，及執行過程。

     如：

    explain select sql_no_cache a.ID,a.MANAGER_NAME,a.MOBILE,a.MANAGER_PHOTO,a.MANAGER_CORP,(ifnull(b.integral_sum,0)+ifnull(c.USER_SCORE,0)+ifnull(d.USER_SCORE,0)) as sumscore  from tb_yytmanager a   LEFT JOIN tb_yyt_integral b ON a.ID = b.userid  LEFT JOIN tb_yyt_userank c ON a.MOBILE=c.USER_MOBILE   LEFT JOIN tb_yyt_userank d  ON a.MOBILE=d.USER_MOBILE   WHERE a.act_type=0 AND c.SCORE_TYPE=2 AND d.SCORE_TYPE=3 group by a.ID order by sumscore desc limit 10;

+----+-------------+-------+------+----------------------------+--------------+---------+--------------+------+----------------------------------------------------+
| id | select_type | table | type | possible_keys              | key          | key_len | ref          | rows | Extra                                              |
+----+-------------+-------+------+----------------------------+--------------+---------+--------------+------+----------------------------------------------------+
|  1 | SIMPLE      | c     | ref  | scoretype,index_SCORE_TYPE | scoretype    | 5       | const        | 2092 | Using temporary; Using filesort                    |
|  1 | SIMPLE      | a     | ref  | PRIMARY,index_mobile       | index_mobile | 153     | func         |    1 | Using index condition; Using where                 |
|  1 | SIMPLE      | b     | ref  | index_userid               | index_userid | 9       | support.a.ID |    1 | NULL                                               |
|  1 | SIMPLE      | d     | ALL  | scoretype,index_SCORE_TYPE | NULL         | NULL    | NULL         | 4166 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------+----------------------------+--------------+---------+--------------+------+----------------------------------------------------+
4 rows in set (0.00 sec)

ALL; 表示全表掃描

2、profile

    profile 可以很清楚的知道每個過程消耗的時間是多少，從而給出優化方向  

    2.1 要使用PROFILE ，應先打開profile選項，

mysql> show variables like 'profiling';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling     | ON    |
+---------------+-------+
1 row in set (0.00 sec)

若沒有打開，可用下面命令 打開

SQL  > SET  profiling=1;

2.2 執行你的SQL

2.3 使用下面命令查看

 mysql> show profile;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| starting             | 0.000159 |
| checking permissions | 0.000009 |
| checking permissions | 0.000003 |
| checking permissions | 0.000003 |
| checking permissions | 0.000006 |
| Opening tables       | 0.000037 |
| init                 | 0.000066 |
| System lock          | 0.000014 |
| optimizing           | 0.000027 |
| statistics           | 0.000155 |
| preparing            | 0.000053 |
| Creating tmp table   | 0.000036 |
| Sorting result       | 0.000006 |
| executing            | 0.000004 |
| Sending data         | 2.208361 |
| Creating sort index  | 0.000619 |
| end                  | 0.000009 |
| removing tmp table   | 0.000363 |
| end                  | 0.000007 |
| query end            | 0.000008 |
| closing tables       | 0.000017 |
| freeing items        | 0.000027 |
| logging slow query   | 0.000070 |
| cleaning up          | 0.000015 |
+----------------------+----------+
24 rows in set, 1 warning (0.00 sec)    

從上可知耗時最多的在Sending data   階段，這樣就可以有針對性的優化了。