mysql> explain select tc.ControlledPCMAC,tc.ControlledPCNickName,tb.CSK300SN,tb.Client_ID from T_BindCSK300 tb left join T_ControlledPC tc on tb.CSK300SN = tc.CSK300SN where tb.Client_ID='6099888bdfe7465098674070d2abd8ff';
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+-------+--------------------------+
| id | select_type | table | type | possible_keys           | key                     | key_len | ref                       | rows  | Extra                    |
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+-------+--------------------------+
|  1 | SIMPLE      | tb    | ref  | index_clientid_csk300sn | index_clientid_csk300sn | 153     | const                     |     1 | Using where; Using index |
|  1 | SIMPLE      | tc    | ref  | index_csk300sn_1        | index_csk300sn_1        | 153     | GoToMyCloudDB.tb.CSK300SN | 18215 |                          |
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+-------+--------------------------+
2 rows in set

mysql> explain select tc.ControlledPCMAC,tc.ControlledPCNickName,tb.CSK300SN,tb.Client_ID from T_BindCSK300 tb left join T_ControlledPC tc on tb.CSK300SN = tc.CSK300SN where tb.Client_ID='6099888bdfe7465098674070d2abd8ff';
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys           | key                     | key_len | ref                       | rows | Extra                    |
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+------+--------------------------+
|  1 | SIMPLE      | tb    | ref  | index_clientid_csk300sn | index_clientid_csk300sn | 153     | const                     |    1 | Using where; Using index |
|  1 | SIMPLE      | tc    | ref  | index_csk300sn          | index_csk300sn          | 153     | GoToMyCloudDB.tb.CSK300SN |  478 |                          |
+----+-------------+-------+------+-------------------------+-------------------------+---------+---------------------------+------+--------------------------+