Comment 3 for bug 860580

EXPLAIN:
+----+-------------+--------------+--------+-------------------------------------+--------------+---------+--------------------+------+-------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+--------------+--------+-------------------------------------+--------------+---------+--------------------+------+-------------------------------------------------+
| 1 | PRIMARY | alias1 | ALL | NULL | NULL | NULL | NULL | 20 | Using temporary; Using filesort |
| 1 | PRIMARY | alias3 | index | NULL | PRIMARY | 4 | NULL | 20 | Using index; Using join buffer (flat, BNL join) |
| 1 | PRIMARY | alias2 | index | NULL | PRIMARY | 4 | NULL | 100 | Using index; Using join buffer (flat, BNL join) |
| 2 | SUBQUERY | SQ2_alias1 | system | PRIMARY | NULL | NULL | NULL | 1 | |
| 2 | SUBQUERY | <subquery3> | eq_ref | distinct_key | distinct_key | 8 | const,const | 1 | |
| 3 | SUBQUERY | C_SQ1_alias3 | range | PRIMARY,col_int_key,col_varchar_key | col_int_key | 4 | NULL | 3 | Using where; Using temporary |
| 3 | SUBQUERY | C_SQ1_alias1 | index | NULL | col_int_key | 4 | NULL | 20 | Using index; Using join buffer (flat, BNL join) |
| 3 | SUBQUERY | C_SQ1_alias2 | eq_ref | PRIMARY,col_varchar_key | PRIMARY | 4 | j0.C_SQ1_alias3.pk | 1 | Using where |
+----+-------------+--------------+--------+-------------------------------------+--------------+---------+--------------------+------+-------------------------------------------------+
8 rows in set (0.02 sec)