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;`
