execute as login 切换上下文

作为DBA，可能经常需要帮助Developer排除有关权限的问题。要确认某个账号是不是已经拥有了某权限，DBA并不需要使用该账号的登录名和密码进行验证，只需使用execute as语句，将当前会话的上下文切换到指定的login（登录）或者user（用户），就可以验证该账号是否拥有某权限。

execute as user='user_name'

该语句模拟的上下文是当前数据库中的user，模拟范围仅限于当前数据库，任何对该数据库以外的资源的访问尝试都会导致失败，不管该user是否拥有相应权限。

execute as login='login_name'

该语句模拟的上下文是一个login，模拟范围处于服务器级别，可以访问当前数据库之外的资源，只要该login拥有相应权限。

select spid,loginame from master..sysprocesses where spid=@@spid

查看当前的登录名和用户名

SELECT SUSER_NAME(), USER_NAME();

USE AdventureWorksLT2008R2;

GO

--Create two temporary principals

CREATE LOGIN login1 WITH PASSWORD = 'J345#$)thb';

CREATE LOGIN login2 WITH PASSWORD = 'Uor80$23b';

GO

CREATE USER user1 FOR LOGIN login1;

CREATE USER user2 FOR LOGIN login2;

GO

--Give IMPERSONATE permissions on user2 to user1

--so that user1 can successfully set the execution context to user2.

GRANT IMPERSONATE ON USER:: user2 TO user1;

--REVOKE IMPERSONATE ON USER:: user2 TO user1;

GO

--Display current execution context.

SELECT SUSER_NAME(), USER_NAME();

-- Set the execution context to login1.

EXECUTE AS LOGIN = 'login1';

--Verify the execution context is now login1.

SELECT SUSER_NAME(), USER_NAME();

--Login1 sets the execution context to login2.

EXECUTE AS USER = 'user2';

--Display current execution context.

SELECT SUSER_NAME(), USER_NAME();

-- The execution context stack now has three principals: the originating caller, login1 and login2.

--The following REVERT statements will reset the execution context to the previous context.

REVERT;

--Display current execution context.

SELECT SUSER_NAME(), USER_NAME();

REVERT;

--Display current execution context.

SELECT SUSER_NAME(), USER_NAME();

--Remove temporary principals.

DROP LOGIN login1;

DROP LOGIN login2;

DROP USER user1;

DROP USER user2;

GO