MariaDB [test]> explain SELECT t1.f6, t1.f6, t1.f3, t1.f4, t1.f7, t1.f8, t1.f9, DATE_FORMAT( t2.f3, '%Y-%m-%d' ), t3.f5 FROM t1 LEFT JOIN t2 ON t2.f1 = t1.f1 AND t2.f3 >= '2015-03-14' AND t2.f3 <= '2015-03-14' LEFT JOIN t3 ON t3.f3=MONTH(t2.f3) ORDER BY t2.f3 limit 300;

+------+-------------+-------+-------+---------------+------+---------+------+--------+------------------------------------------------+

| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows   | Extra                                          |

+------+-------------+-------+-------+---------------+------+---------+------+--------+------------------------------------------------+

|    1 | SIMPLE      | t1    | ALL   | NULL          | NULL | NULL    | NULL | 110000 | Using temporary; Using filesort                |

|    1 | SIMPLE      | t2    | range | idx1,idx2     | idx2 | 3       | NULL |   1117 | Range checked for each record (index map: 0x6) |

|    1 | SIMPLE      | t3    | ref   | idx3          | idx3 | 4       | func |   1477 | Using where                                    |

+------+-------------+-------+-------+---------------+------+---------+------+--------+------------------------------------------------+

3 rows in set (0.00 sec)

MariaDB [test]> explain SELECT t1.f6, t1.f6, t1.f3, t1.f4, t1.f7, t1.f8, t1.f9, DATE_FORMAT( t2.f3, '%Y-%m-%d' ), t3.f5 FROM t1 LEFT JOIN t2 force index(idx2) ON t2.f1 = t1.f1 AND t2.f3 >= '2015-03-14' AND t2.f3 <= '2015-03-14' LEFT JOIN t3 ON t3.f3=MONTH(t2.f3) ORDER BY t2.f3 limit 300;

+------+-------------+-------+-------+---------------+------+---------+------+--------+-------------------------------------------------+

| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows   | Extra                                           |

+------+-------------+-------+-------+---------------+------+---------+------+--------+-------------------------------------------------+

|    1 | SIMPLE      | t1    | ALL   | NULL          | NULL | NULL    | NULL | 110000 | Using temporary; Using filesort                 |

|    1 | SIMPLE      | t2    | range | idx2          | idx2 | 3       | NULL |   1117 | Using where; Using join buffer (flat, BNL join) |

|    1 | SIMPLE      | t3    | ref   | idx3          | idx3 | 4       | func |   1477 | Using where                                     |

+------+-------------+-------+-------+---------------+------+---------+------+--------+-------------------------------------------------+