--创建登录账号

create login username with password='password'

--创建数据库用户

create user username for login username

---授予该用户对Student表的查询权限，同时授予其进一步授权其他用户的权利。

grant select

on student

to user_tom

with grant option

-----

create login marry with password='marry001'

create user user_marry for login marry

--创建角色

create role dbnormuser

---对角色授权

grant select

on student

to dbnormuser

--指定固定的服务器角色（登录名）

sp_addsrvrolemember marry,sysadmin

删除

 sp_dropsrvrolemember marry,sysadmin

--查看用户

sp_helpuser

---新建外键约束

ALTER TABLE test_sub ADD CONSTRAINT main_id_cons FOREIGN KEY (main_id) REFERENCES test_main;

---删除外键

ALTER TABLE test_sub drop CONSTRAINT main_id_cons

--创建级联删除外键

ALTER TABLE test_sub ADD CONSTRAINT main_id_cons FOREIGN KEY (main_id) REFERENCES test_main on delete

cascade

--创建级联更新外键

ALTER TABLE test_sub ADD CONSTRAINT main_id_cons FOREIGN KEY (main_id) REFERENCES test_main on update

cascade

--创建删除被参照主键是 键参照关系的外键设置为null

ALTER TABLE test_sub ADD CONSTRAINT main_id_cons FOREIGN KEY (main_id) REFERENCES test_main on update

set null

----参照完整性

不能删除 带有外键的记录