此时情况下根据MySQL的最左前缀原则, first_name 可以使用索引，last_name采用了like 模糊查询，不能使用索引。
c 关闭ICP
mysql> set optimizer_switch='index_condition_pushdown=off';
Query OK, 0 rows affected (0.00 sec)
mysql> SET profiling = 1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> select * from employees where first_name='Anneke' and last_name like '%sig' ;
+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date |
+--------+------------+------------+-----------+--------+------------+
| 10006 | 1953-04-20 | Anneke | Preusig | F | 1989-06-02 |
+--------+------------+------------+-----------+--------+------------+
1 row in set (0.00 sec)
mysql> SET profiling = 0;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> show profiles;
+----------+------------+--------------------------------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+--------------------------------------------------------------------------------+
| 2 | 0.00097000 | select * from employees where first_name='Anneke' and last_name like '%sig' |
+----------+------------+--------------------------------------------------------------------------------+
6 rows in set, 1 warning (0.00 sec)
当开启ICP时 查询在sending data环节时间消耗是 0.000189s
mysql> show profile cpu,block io for query 1;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000094 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000025 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000044 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000014 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.000093 | 0.000000 | 0.000000 | 0 | 0 |
| preparing | 0.000024 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.000189 | 0.000000 | 0.000000 | 0 | 0 |
| end | 0.000019 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000034 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
15 rows in set, 1 warning (0.00 sec)
