2
CREATE TABLE IF NOT EXISTS `tx_hep_homes_attributes_mm` (
`uid_local` int(11) NOT NULL DEFAULT '0',
`uid_foreign` int(11) NOT NULL DEFAULT '0',
`tablenames` varchar(30) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
`sorting` int(11) NOT NULL DEFAULT '0',
KEY `uid_local` (`uid_local`),
KEY `uid_foreign` (`uid_foreign`),
KEY `uid_local_foreign` (`uid_local`,`uid_foreign`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
样品输入:
INSERT INTO `tx_hep_homes_attributes_mm` (`uid_local`, `uid_foreign`, `tablenames`, `sorting`) VALUES
(2, 4, '', 3),
(2, 1, '', 2),
(2, 2, '', 1),
(1, 2, '', 5),
(1, 3, '', 4),
(1, 4, '', 3),
(1, 7, '', 2),
(1, 8, '', 1);
查询:
SELECT amm.uid_local,
amm.uid_foreign
FROM tx_hep_homes_attributes_mm amm
JOIN (SELECT 1 AS att_id
UNION
SELECT 4 AS att_id
UNION
SELECT 13 AS att_id
UNION
SELECT 22 AS att_id
UNION
SELECT 12 AS att_id)d1
ON d1.att_id = amm.uid_foreign
JOIN (SELECT 1 AS home_id
UNION
SELECT 2 AS home_id)d2
ON d2.home_id = amm.uid_local
ORDER BY uid_local
生产:
+------+---------------+-------------------+-------+------------------------------------------+--------------------+----------+-------------+-------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+---------------+-------------------+-------+------------------------------------------+--------------------+----------+-------------+-------+---------------------------------+
| 1 | PRIMARY | <derived7> | ALL | NULL | NULL | NULL | NULL | 2 | Using temporary; Using filesort |
| 1 | PRIMARY | amm | ref | uid_local,uid_foreign,uid_local_foreign | uid_local_foreign | 4 | d2.home_id | 1 | Using where; Using index |
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 5 | Using where; Using join buffer |
| 7 | DERIVED | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| 8 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| NULL | UNION RESULT | <union7,8> | ALL | NULL | NULL | NULL | NULL | NULL | |
| 2 | DERIVED | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| 3 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| 4 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| 5 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| 6 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
| NULL | UNION RESULT | <union2,3,4,5,6> | ALL | NULL | NULL | NULL | NULL | NULL | |
+------+---------------+-------------------+-------+------------------------------------------+--------------------+----------+-------------+-------+---------------------------------+
正如你所看到的那样,使用文件排序,尽管它应该从复合索引中解析出来。
此表为示例数据,这就是为什么它只有9行。但解释仍然需要展示最佳匹配。 – Pentium10 2012-01-03 13:58:57
这取决于数据的大小和结果中需要的行数,因此您必须查看实际数据。 – Mark 2012-01-03 14:01:21
如果索引基数较低或者行数为小。 9很小。 – 2012-01-03 14:09:16