联合索引特殊案例

CREATE TABLE t(
varchar(10) not null,
varchar(10) not null,
varchar(10) not null,
varchar(10) not null,
varchar(10) not null
)ENGINE InnoDB CHARSET UTF8;
    
alter table t add index c1234(c1,c2,c3,c4);
   
insertintoVALUES('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'1' and'1' and'1';

 案例2：between也不影响走四个

explain select * from t where c1 between'1' and'3' and'1' and'1' and'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';