4
我见过很多类似的问题,但是我没有看到适用于我的解决方案。或者,也许我正在密集。 :)希望有人能帮助我。MYSQL在简单查询中使用ORDER BY索引列时使用filesort
我有如下表:
CREATE TABLE `table_name` (
`value1` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`value2` varchar(50) NOT NULL,
`value3` tinytext,
`value4` tinytext,
`value5` tinytext,
`value6` char(3) DEFAULT NULL,
`value7` char(3) DEFAULT NULL,
PRIMARY KEY (`value1`),
KEY value2_index ('value2')
) ENGINE=MyISAM AUTO_INCREMENT=46 DEFAULT CHARSET=latin1;
为了验证我的指标进行设置,这是SHOW INDEX结果:
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| table_name | 0 | PRIMARY | 1 | value1 | A | 43 | NULL | NULL | | BTREE | |
| table_name | 1 | value2_index | 1 | value2 | A | NULL | NULL | NULL | YES | BTREE | |
+--------------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2 rows in set (0.00 sec)
当我运行此查询:
SELECT value2, value6
FROM table_name
WHERE value7 = 'Yes'
ORDER BY value2;
我认为通过在value2上添加一个索引,它会停止使用filesort的查询。然而,EXPLAIN显示方式不同:
+----+-------------+--------------+------+---------------+------+---------+------+------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+--------------+------+---------------+------+---------+------+------+-----------------------------+
| 1 | SIMPLE | table_name | ALL | NULL | NULL | NULL | NULL | 43 | Using where; Using filesort |
+----+-------------+--------------+------+---------------+------+---------+------+------+-----------------------------+
1 row in set (0.00 sec)
我在做什么错?
谢谢!