联合索引特殊案例
作者：互联网
CREATE TABLE t(
c1 varchar(10) not null,
c2 varchar(10) not null,
c3 varchar(10) not null,
c4 varchar(10) not null,
c5 varchar(10) not null
)ENGINE InnoDB CHARSET UTF8;
alter table t add index c1234(c1,c2,c3,c4);
insert into t VALUES('1','1','1','1','1'),('2','2','2','2','2'),('3','3','3','3','3'),('4','4','4','4','4'),('5','5','5','5','5');
案例1：不影响索引走四个
explain select * from t where c1 like '3' and c2 = '1' and c3 = '1' and c4 = '1';
案例2：between也不影响走四个
explain select * from t where c1 between '1' and '3' and c2 = '1' and c3 = '1' and c4 = '1';
案例3：走一个 c1索引
explain select * from t where c1 > '3' and c2 = '1' and c3 = '1' and c4 = '1';
案例4：走c1,c2两个索引
explain select * from t where c1 = '1' and c2 > '1' and c3 = '1' and c4 = '1';
标签：特殊,varchar,案例,索引,c3,c2,c1,null,c4 来源： https://www.cnblogs.com/SunshineKimi/p/16530828.html