新建一个索引能够同时提升三条SQL的查询性能

如题

CREATE TABLE `score` (  `id` int(11) NOT NULL,  `studentid` int(11) NOT NULL,  `subjectid` int(11) NOT NULL,  `score` int(11) NOT NULL,  PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;-- 新建一个索引能够同时提升三条SQL的查询性能ALTER TABLE `score` ADD INDEX `score` ( `score` , `studentid` , `subjectid` )EXPLAIN SELECT * FROM score WHERE score=100;EXPLAIN SELECT * FROM score WHERE studentid=5 AND score=100;EXPLAIN SELECT * FROM score WHERE studentid=5 AND subjectid=2 AND score=100;

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