今天公司SQL Server数据库无意间变为SINGLE_USER模式了，而且使用如下语句切换回MULTI_USER失败：
ALTER DATABASE [MyDB] SET MULTI_USER WITH ROLLBACK IMMEDIATE
报错：
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.
该错误提示是有其它用户在使用数据库，没办法只好排查是谁：
1）通过sys.sysprocesses或者sys.dm_exec_sessions，或者存储过程sp_who，然后用KILL命令把会话切断
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）如果上面还是行不通，再检查sys.dm_tran_locks，然后用KILL命令把会话切断
select * from sys.dm_tran_locks where resource_database_id= DB_ID (‘MyDB‘)
kill 148
无法将数据库从SINGLE_USER模式切换回MULTI_USER模式（Error 5064）
原文：https://www.cnblogs.com/OpenCoder/p/10037560.html