mysql 组合索引中对范围的查询

建立表：

CREATE TABLE `ygzt_test` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`a` int(11) NOT NULL,
`b` int(11) NOT NULL,
`c` int(11) NOT NULL,
`d` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `a` (`a`,`b`,`c`,`d`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci COMMENT=‘测试‘;

一、实验一，无order by

首先加联合索引a,b,c,d

explain select * from ygzt_test where a=1 and b=2 and c=3 and d=4

修改sql：

explain select * from ygzt_test where a>1 and b=2 and c=3 and d=4

type已经由ref降为index

修改索引b,c,d,a

explain select * from ygzt_test where a>1 and b=2 and c=3 and d=4

done

二、实验二，order by

建立索引a，b

explain select * from ygzt_test where a>0 order by b

可以看到，a>0使用了索引，order by b 未使用

修改索引为b，a

explain select * from ygzt_test where a>0   order by b

where 与 order by 都无索引

想起此前order by＋select ＊的问题

这个问题单独拿出来实践下：

修改索引为a

explain select * from ygzt_test order by a

explain select * from ygzt_test FORCE INDEX (a)  order by a

结论：

1.单列索引中——<,<=,=,>,>=,between,like（右边模糊）适用索引

2.索引中有范围的，有序性失效，解决方案以实际为准