mysql> drop table if exists `t1`;
Query OK, 0 rows affected (0.00 sec)

mysql> create table `t1`(`c` int)engine=myisam;
Query OK, 0 rows affected (0.02 sec)

mysql> insert into `t1` values (),();
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> drop table if exists `t2`;
Query OK, 0 rows affected (0.00 sec)

mysql> create table `t2` (
    -> `b` int,
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`),key(`b`),key(`b`),
    -> key(`b`),key(`b`),key(`b`))engine=myisam;
Query OK, 0 rows affected (0.01 sec)

mysql>
mysql> insert into `t2` values (),(),();
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql>
mysql> explain
    -> select 1
    -> from
    -> (select 1 from `t2`,`t1` where `b` < `c` group by 1 limit 1) as `d2`
    -> ;
+----+-------------+------------+--------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+------+---------+------+------+--------------------------------------------------------+
| id | select_type | table      | type   | possible_keys                                                                                                                                             | key  | key_len | ref  | rows | Extra                                                  |
+----+-------------+------------+--------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+------+---------+------+------+--------------------------------------------------------+
|  1 | PRIMARY     | <derived2> | system | NULL                                                                                                                                                      | NULL | NULL    | NULL |    0 | const row not found                                    |
|  2 | DERIVED     | t1         | ALL    | NULL                                                                                                                                                      | NULL | NULL    | NULL |    2 |                                                        |
|  2 | DERIVED     | t2         | range  | b,b_2,b_3,b_4,b_5,b_6,b_7,b_8,b_9,b_10,b_11,b_12,b_13,b_14,b_15,b_16,b_17,b_18,b_19,b_20,b_21,b_22,b_23,b_24,b_25,b_26,b_27,b_28,b_29,b_30,b_31,b_32,b_33 | b    | 5       | NULL |    0 | Range checked for each record (index map: 0x1FFFFFFFF) |
+----+-------------+------------+--------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+------+---------+------+------+--------------------------------------------------------+
3 rows in set (0.00 sec)

mysql>
mysql>