MySQL学习--普通索引

在创建表时创建索引，已有表创建索引，alter table创建索引

1.在创建表时创建索引

create table emp(

ename varchar(20),

deptno int(10) primary key auto_increment,

index index_niu(deptno)

);

explain select * from emp where deptno=22;

 

2.已有表创建索引

create table emp(

ename varchar(20),

deptno int(10) primary key auto_increment

);

create index index_niu on emp(deptno);

explain select * from emp where deptno=22;

 

3.alter table创建索引

alter table emp add index index_niu(deptno);

 

4.删除索引

drop index index_niu on emp;