今天公司SQL Server資料庫無意間變為SINGLE_USER模式了，而且使用如下語句切換回MULTI_USER失敗：

ALTER DATABASE [MyDB] SET MULTI_USER  WITH ROLLBACK IMMEDIATE 

報錯：

Msg 5064, Level 16, State 1, Line 1
Changes to the state or options of database 'MyDB' cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.

該錯誤提示是有其它使用者在使用資料庫，沒辦法只好排查是誰：

1）通過sys.sysprocesses或者sys.dm_exec_sessions，或者儲存過程sp_who，然後用KILL命令把會話切斷

select * from sys.sysprocesses 
where spid > 50
And dbid=DB_ID ('MyDB')

SELECT * FROM sys.dm_exec_sessions
WHERE database_id = DB_ID ('MyDB')

2）如果上面還是行不通，再檢查sys.dm_tran_locks，然後用KILL命令把會話切斷

select * from sys.dm_tran_locks where resource_database_id= DB_ID ('MyDB')

kill 148