+----+--------------------+----------------+-----------------+--------------------+------------+---------+----------------------+--------+--------------------------+
| id | select_type        | table          | type            | possible_keys      | key        | key_len | ref                  | rows   | Extra                    |
+----+--------------------+----------------+-----------------+--------------------+------------+---------+----------------------+--------+--------------------------+
|  1 | PRIMARY            | a              | ALL             | MerchantID         | NULL       |    NULL | NULL                 | 169870 | Using where              |
|  1 | PRIMARY            | b              | ref             | PRIMARY,MerchantID | MerchantID |       4 | product.a.MerchantID |      1 |                          |
|  2 | DEPENDENT SUBQUERY | Cat_919_Search | unique_subquery | PRIMARY,SearchStr  | PRIMARY    |       4 | func                 |      1 | Using index; Using where |
+----+--------------------+----------------+-----------------+--------------------+------------+---------+----------------------+--------+--------------------------+