Untitled

+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| id   | select_type  | table      | type  | possible_keys | key    | key_len | ref  | rows   | Extra                                                     |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| 1    | PRIMARY      | u          | range | idx_u         | idx_u  | 9       | NULL | 26157  | Using where; Using index; Using temporary; Using filesort |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| 1    | PRIMARY      | <derived2> | ALL   | NULL          | NULL   | NULL    | NULL | 50586  | Using where                                               |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| 2    | DERIVED      | <derived3> | ALL   | NULL          | NULL   | NULL    | NULL | 208600 | Using temporary; Using filesort                           |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| 3    | DERIVED      | match      | range | idx_m1,idx_m2 | idx_m1 | 9       | NULL | 104129 | Using where; Using index                                  |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| 4    | UNION        | match      | range | idx_m1,idx_m2 | idx_m2 | 9       | NULL | 104129 | Using where; Using index                                  |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+
| NULL | UNION RESULT | <union3,4> | ALL   | NULL          | NULL   | NULL    | NULL | NULL   |                                                           |
+------+--------------+------------+-------+---------------+--------+---------+------+--------+-----------------------------------------------------------+