mysql explain用法

索引是mysql的必须要掌握的技能，同时也是提供mysql查询效率的手段。

最左原则

1、用户表一张，有uid ,user_name,real_name ,eamil等字段，详细见建表语句2、在user_name字段下增加一个简单索引user_name，在email,mobile，age三个字段下增加索引complex_index3、表引擎使用MyISAM，增加4、准备97000条数据（具体的可以根据实际情况来定数据量，这里准备的是97000+）5、实验工具Navcat

DROP TABLE IF EXISTS `qz_users`;CREATE TABLE `qz_users` (  `uid` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '用户的 UID',  `user_name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '用户名',  `real_name` varchar(128) CHARACTER SET utf8 DEFAULT NULL COMMENT '用户姓名',  `email` varchar(255) CHARACTER SET utf8 DEFAULT NULL COMMENT 'EMAIL',  `mobile` varchar(16) CHARACTER SET utf8 DEFAULT NULL COMMENT '用户手机',  `password` varchar(32) CHARACTER SET utf8 DEFAULT NULL COMMENT '用户密码',  `salt` varchar(16) CHARACTER SET utf8 DEFAULT NULL COMMENT '用户附加混淆码',  `avatar_file` varchar(128) CHARACTER SET utf8 DEFAULT NULL COMMENT '头像文件',  `sex` tinyint(1) DEFAULT NULL COMMENT '性别',  `birthday` int(10) DEFAULT NULL COMMENT '生日',  PRIMARY KEY (`uid`),  KEY `user_name` (`user_name`(250)),  KEY `complex_index` (`email`,`mobile`,`sex`)) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

explain select * from qz_users where user_name = "ryanhe";//有索引explain select * from qz_users where email = "x";
//有索引
explain select * from qz_users where email = "x" and mobile = "x" and sex=1;
//有索引
explain select * from qz_users where email = "x" and mobile = "x";
//有索引
explain select * from qz_users where email = "x" and sex = "x";
//有索引
explain select * from qz_users where sex = "x" and mobile = "x";
//无索引
explain select * from qz_users where mobile = "x" and sex = "0";
//无索引


具体地址 https://segmentfault.com/a/1190000008919846