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Mysql目录失效(备忘)

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Jun 07, 2016 pm 04:23 PM

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Mysql索引失效(备忘) ? ? 创建一个user表: CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(32) DEFAULT '', `age` tinyint(4) DEFAULT NULL, `email` varchar(128) DEFAULT NULL, `title` varchar(256) DEFAULT NULL, PRIMARY

Mysql索引失效(备忘)

? ? 创建一个user表:

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(32) DEFAULT '',
  `age` tinyint(4) DEFAULT NULL,
  `email` varchar(128) DEFAULT NULL,
  `title` varchar(256) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`) USING BTREE,
  KEY `age` (`age`),
  KEY `email` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8

? ?其中,'name'为唯一索引,'age'和'email'为普通索引,'title'未使用索引.

1. '!='操作

?
? ? ?三条sql只有一点区别,就是select返回的列信息不同,我们发现,第二条sql使用到了索引,而第一条则没有,看样子"!="操作使索引失效,是有前提的,即返回的结果中,如果只包含"name"是使用索引的.第三条sql因为age是索引列,索引使用到了索引.

2. "in" 操作

? ? 情况和1)非常类似,到底是什么原因?

Statement

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