not null，以及not null和default区别

create table student5
(

stu_id int primary key,
stu_email nvarchar(200) not null,
stu_name nvarchar(20) unique,
stu_sal int check (stu_sal>=1000 and stu_sal<=8000),
stu_sex nchar(1) default '男'

)

insert student5 values(1,'hb.g@163.com','zhangsan',5000);--error
insert student5 (stu_id,stu_email,stu_name,stu_sal) values(2,'hb.g@163.com','zhangsan',5000);
select * from student5

insert student5 (stu_id,stu_email,stu_sal) values(2,'hb.g@163.com',5000);
--stu_name默认是null 也就是说如果一个字段不写null 也不写not null 默认是null
--null和default都允许用户不赋值 nul修饰的字段如果不赋值则默认null default修饰字段不赋值则默认是default指定的值