mysql 組合索引中對範圍的查詢
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=‘測試‘;
一、實驗一，無order by
首先加聯合索引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已經由ref降為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、實驗二，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
修改索引為b，a
explain select * from ygzt_test where a>0 order by b
where 與 order by 都無索引
想起此前order by＋select ＊的問題
這個問題單獨拿出來實踐下：
修改索引為a
explain select * from ygzt_test order by a
explain select * from ygzt_test FORCE INDEX (a) order by a
結論：
1.單列索引中——<,<=,=,>,>=,between,like（右邊模糊）適用索引
2.索引中有範圍的，有序性失效，解決方案以實際為準
mysql 組合索引中對範圍的查詢