MySQL5.0版本之后开放了profiling功能，通过此功能可以查询某个SQL的详细执行计划。
1、开启profiling
mysql> show variables like '%profil%';
+------------------------+-------+
| Variable_name | Value |
+------------------------+-------+
| have_profiling | YES|
| profiling| ON|
| profiling_history_size | 15|
+------------------------+-------+
2、执行SQL，进行测试
mysql> select * from xcredit.tb_sync_job_bak;
3、查看profiles
mysql> show profiles;
+----------+------------+------------------------------------------------------------------------------+
| Query_ID | Duration| Query|
+----------+------------+------------------------------------------------------------------------------+
|1 | 0.00009600 | set global profiling=1|
|2 | 0.00218100 | show variables like '%profil%'|
|3 | 0.04091100 | select * from xcredit.tb_sync_job_bak where lid<1000 group by lid limit 5000 |
|4 | 0.00019800 | select * from xcredit.tb_sync_job_bak where lid<1000 group by lid|
|5 | 0.16355550 | select * from xcredit.tb_sync_job_bak where lid<1000 |
|6 | 0.00230025 | show variables like '%profil%'|
|7 | 0.00014375 | select * from xcredit.tb_sync_job_bak group by lid%20 order by lid|
|8 | 0.00013600 | select * from xcredit.tb_sync_job_bak group by lid%20 order by 1 |
|9 | 0.00013375 | select * from xcredit.tb_sync_job_bak group by lid%20|
|10 | 0.26594500 | select * from xcredit.tb_sync_job_bak|
+----------+------------+------------------------------------------------------------------------------+
4、查看执行计划
mysql> show profile for query 10;
+----------------------+----------+
| Status| Duration |
+----------------------+----------+
| starting | 0.000053 |
| checking permissions | 0.000005 |
| Opening tables| 0.000014 |
| init | 0.000014 |
| System lock | 0.000006 |
| optimizing| 0.000003 |
| statistics| 0.000010 |
| preparing| 0.000009 |
| executing| 0.000001 |
| Sending data | 0.265498 |
| end | 0.000009 |
| query end| 0.000010 |
| closing tables| 0.000008 |
| freeing items| 0.000258 |
| logging slow query| 0.000036 |
| cleaning up | 0.000011 |
+----------------------+----------+
此查询返回八万多行数据，返回数据量较大，因此出现sending data。