Exiting single-user mode in MSSQL

USE master;
GO

DECLARE @sql nvarchar(max) = N'';

SELECT @sql += CAST(N'KILL ' + CAST(session_id AS nvarchar(10)) + N';' AS nvarchar(max))
FROM sys.dm_exec_sessions
WHERE database_id = DB_ID(N'DeineDatenbank')
  AND session_id <> @@SPID;

EXEC sp_executesql @sql;

ALTER DATABASE [DeineDatenbank]
SET MULTI_USER;
GO