把这个profiling功能打开，可以查看sql查询语句的整个过程中各种资源的消耗情况。

mysql> show profiles;
+----------+------------+---------------------------------+
| Query_ID | Duration   | Query                           |
+----------+------------+---------------------------------+
|        1 | 0.00049600 | show variables like "profiling" |
|        2 | 0.02267400 | show databases                  |
|        3 | 0.04235200 | SELECT DATABASE()               |
|        4 | 0.00012825 | SELECT DATABASE()               |
|        5 | 0.00025125 | show databases                  |
|        6 | 0.00145125 | show tables                     |
|        7 | 0.04207925 | show tables                     |
|        8 | 0.03485225 | select count(*) from host_item  |
+----------+------------+---------------------------------+

mysql> show profile cpu, block io  for query 8;
+----------------------+----------+----------+------------+--------------+---------------+
| Status               | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting             | 0.000634 | 0.000000 |   0.000000 |            0 |             0 |
| checking permissions | 0.000013 | 0.000000 |   0.000000 |            0 |             0 |
| Opening tables       | 0.000051 | 0.000000 |   0.000000 |            0 |             0 |
| System lock          | 0.000014 | 0.000000 |   0.000000 |            0 |             0 |
| init                 | 0.000015 | 0.000000 |   0.000000 |            0 |             0 |
| optimizing           | 0.033657 | 0.000000 |   0.000000 |           40 |             0 |
| statistics           | 0.000029 | 0.000000 |   0.000000 |            0 |             0 |
| preparing            | 0.000012 | 0.000000 |   0.000000 |            0 |             0 |
| executing            | 0.000006 | 0.000000 |   0.000000 |            0 |             0 |
| Sending data         | 0.000313 | 0.000000 |   0.000000 |            0 |             0 |
| end                  | 0.000008 | 0.000000 |   0.000000 |            0 |             0 |
| query end            | 0.000008 | 0.000000 |   0.000000 |            0 |             0 |
| closing tables       | 0.000047 | 0.000000 |   0.000000 |            0 |             0 |
| freeing items        | 0.000042 | 0.000000 |   0.000000 |            0 |             0 |
| logging slow query   | 0.000003 | 0.000000 |   0.000000 |            0 |             0 |
| cleaning up          | 0.000003 | 0.000000 |   0.000000 |            0 |             0 |
+----------------------+----------+----------+------------+--------------+---------------

show profile后面可以跟参数：all或者cpu,block io,page faults等。

也可以在information_schema.profiling数据库表中直接查询：

select state,sum(duration) as total_r,round(100*sum(duration)/(select sum(duration) from information_schema.profiling where query_id=@query_id),2) as pct_r,count(*) as calls,sum(duration)/count(*) as "r/call" from information_schema.profiling where query_id=@query_id group by state order by total_r desc;

最后，关闭set profiling=0该功能。

本文出自 “Victor的奋斗历程” 博客，请务必保留此出处http://victor2016.blog.51cto.com/6768693/1875012

mysql查询语句优化工具