mysql> explain SELECT id
-> FROM file
-> WHERE size IN
-> ( SELECT size FROM tmpTab );
+----+--------------------+--------+-------+---------------+----------+---------
+------+-------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len
| ref | rows | Extra |
+----+--------------------+--------+-------+---------------+----------+---------
+------+-------+--------------------------+
| 1 | PRIMARY | file | index | NULL | filesize | 8
| NULL | 21168 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | tmpTab | ALL | NULL | NULL | NULL
| NULL | 3197 | Using where |
+----+--------------------+--------+-------+---------------+----------+---------
+------+-------+--------------------------+
2 rows in set (0.00 sec)