我正在运行一个使用类似于下表的表的应用程序。有一个用于文章的表,还有另一个用于标签的表。我想按文章 ID 获取特定标签订单的最新 30 篇文章。例如“acer”,下面的查询将完成这项工作,但它没有正确索引,因为如果有很多与特定标签相关的文章,它将扫描很多行。如何运行查询以获得相同的结果而不扫描大量行?
EXPLAIN SELECT title
FROM tag, article
WHERE tag = 'acer'
AND tag.article_id = article.id
ORDER BY tag.article_id DESC
LIMIT 0 , 30
Output
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE tag ref tag tag 92 const 220439 Using where; Using index
1 SIMPLE article eq_ref PRIMARY PRIMARY 4 testdb.tag.article_id 1
以下是表格和样本数据:
CREATE TABLE `article` (
`id` int(11) NOT NULL auto_increment,
`title` varchar(60) NOT NULL,
`time_stamp` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1000001 ;
--
-- Dumping data for table `article`
--
INSERT INTO `article` VALUES (1, 'Saudi Apple type D', 1313390211);
INSERT INTO `article` VALUES (2, 'Japan Apple type A', 1313420771);
INSERT INTO `article` VALUES (3, 'UAE Samsung type B', 1313423082);
INSERT INTO `article` VALUES (4, 'UAE Apple type H', 1313417337);
INSERT INTO `article` VALUES (5, 'Japan Samsung type D', 1313398875);
INSERT INTO `article` VALUES (6, 'UK Acer type B', 1313387888);
INSERT INTO `article` VALUES (7, 'Saudi Sony type D', 1313429416);
INSERT INTO `article` VALUES (8, 'UK Apple type B', 1313394549);
INSERT INTO `article` VALUES (9, 'Japan HP type A', 1313427730);
INSERT INTO `article` VALUES (10, 'Japan Acer type C', 1313400046);
CREATE TABLE `tag` (
`tag` varchar(30) NOT NULL,
`article_id` int(11) NOT NULL,
UNIQUE KEY `tag` (`tag`,`article_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
--
-- Dumping data for table `tag`
--
INSERT INTO `tag` VALUES ('Samsung', 1);
INSERT INTO `tag` VALUES ('Acer', 2);
INSERT INTO `tag` VALUES ('Sony', 3);
INSERT INTO `tag` VALUES ('Apple', 4);
INSERT INTO `tag` VALUES ('Acer', 5);
INSERT INTO `tag` VALUES ('HP', 6);
INSERT INTO `tag` VALUES ('Acer', 7);
INSERT INTO `tag` VALUES ('Sony', 7);
INSERT INTO `tag` VALUES ('Acer', 7);
INSERT INTO `tag` VALUES ('Samsung', 9);