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。