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;
樣品輸入:
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);
查詢:
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
生產:
+------+---------------+-------------------+-------+------------------------------------------+--------------------+----------+-------------+-------+---------------------------------+
| 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 | |
+------+---------------+-------------------+-------+------------------------------------------+--------------------+----------+-------------+-------+---------------------------------+
正如你所看到的那樣,使用文件排序,儘管它應該從複合索引中解析出來。
此表爲示例數據,這就是爲什麼它只有9行。但解釋仍然需要展示最佳匹配。 – Pentium10 2012-01-03 13:58:57
這取決於數據的大小和結果中需要的行數,因此您必須查看實際數據。 – Mark 2012-01-03 14:01:21
如果索引基數較低或者行數爲小。 9很小。 – 2012-01-03 14:09:16