当用人问你MySQL 查询条件中 in 会不会用到索引,你该怎么回答?
答案:可能会用到索引
动手来测试下
1.创建一张表,给字段port建立索引
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CREATE TABLE `pre_request_logs_20180524` (
`id` int (11) NOT NULL AUTO_INCREMENT,
`ip` char (16) NOT NULL COMMENT '代理IP' ,
`port` int (8) NOT NULL COMMENT '端口号' ,
`status` enum( '成功' , '失败' ) NOT NULL COMMENT '状态' ,
`create_time` datetime NOT NULL COMMENT '创建时间' ,
`update_time` datetime DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP ,
PRIMARY KEY (`id`),
KEY `idx_port` (`port`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8 COMMENT= '代理IP请求日志' ;
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插入测试数据
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INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (1, '192.168.1.199' , 53149, '失败' , '2018-05-24 14:55:34' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (2, '192.168.1.100' , 10653, '成功' , '2018-05-24 14:55:54' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (3, '192.168.1.112' , 50359, '失败' , '2018-05-24 14:56:00' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (4, '192.168.1.67' , 30426, '失败' , '2018-05-24 14:56:09' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (5, '192.168.1.209' , 49323, '失败' , '2018-05-24 14:56:12' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (6, '192.168.1.209' , 51161, '成功' , '2018-05-24 14:56:13' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (7, '192.168.1.12' , 54167, '成功' , '2018-05-24 14:56:16' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (8, '192.168.1.64' , 20462, '成功' , '2018-05-24 14:56:19' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (9, '192.168.1.53' , 22823, '失败' , '2018-05-24 14:56:31' , '2018-11-16 10:58:13' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (10, '192.168.1.85' , 48229, '成功' , '2018-05-24 14:56:32' , '2018-11-16 11:01:11' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (11, '192.168.1.85' , 48229, '成功' , '2018-05-24 14:56:32' , '2018-11-16 11:01:15' );
INSERT INTO ``(`id`, `ip`, `port`, `status`, `create_time`, `update_time`) VALUES (12, '192.168.1.85' , 48229, '成功' , '2018-05-24 14:56:32' , '2018-11-16 13:34:37' );
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2.测试sql
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explain select * from pre_request_logs_20180524 where port in (51161,20462,48229);
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执行结果
从结果来看是没有用到索引,但不要着急下结论,再看二个sql
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select * from pre_request_logs_20180524 where port in (51161,48229);
select * from pre_request_logs_20180524 where port in (51161,20462);
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执行结果分别如下
可以看到第二条sql是用到了索引,二条sql的区别在于port值不一样,一个包含48229,一个包含20462
其实MySQL优化器会自动判断in是否走二级索引,也就是port字段的索引
总结
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,谢谢大家对服务器之家的支持。
原文链接:https://segmentfault.com/a/1190000019804419