mysql in

result.txt

mysql> show columns in `order`;
+----------+---------+------+-----+---------+----------------+
| Field    | Type    | Null | Key | Default | Extra          |
+----------+---------+------+-----+---------+----------------+
| id       | int(11) | NO   | PRI | NULL    | auto_increment |
| product  | int(11) | NO   |     | NULL    |                |
| quantity | int(11) | NO   |     | NULL    |                |
+----------+---------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

mysql> show columns in `product`;
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| category | int(11)     | NO   | MUL | NULL    |                |
| name     | varchar(20) | NO   |     | NULL    |                |
+----------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> explain select * from `order` where id in (select id from product where category = 4);
+----+-------------+---------+------------+--------+----------------------+---------+---------+---------------+------+----------+-------------+
| id | select_type | table   | partitions | type   | possible_keys        | key     | key_len | ref           | rows | filtered | Extra       |
+----+-------------+---------+------------+--------+----------------------+---------+---------+---------------+------+----------+-------------+
|  1 | SIMPLE      | order   | NULL       | ALL    | PRIMARY              | NULL    | NULL    | NULL          |    1 |   100.00 | NULL        |
|  1 | SIMPLE      | product | NULL       | eq_ref | PRIMARY,idx_category | PRIMARY | 4       | test.order.id |    1 |   100.00 | Using where |
+----+-------------+---------+------------+--------+----------------------+---------+---------+---------------+------+----------+-------------+
2 rows in set, 1 warning (0.01 sec)