【笔记】5. 非空和唯一约束

create table mydb1.emp(
	eid int primary key,
	name varchar(20) unique,
	deptID int not null,
	salary double
	);
	
insert into mydb1.emp values
(1,'zhangsan',1,2000),
(2,'zhangsan',2,1000),
(3,'wangwu',3,4000);

alter table mydb1.emp modify deptID int; #删除非空
alter table mydb1.emp modify deptID int not null;

alter table mydb1.emp drop index name; #删除unique

drop table emp