如果RECOVERY是SIMPLE，直接收缩，否则先切换为SIMPLE，再收缩。

    USE[master]
    GO

    ALTER DATABASE DBName SET RECOVERY SIMPLE WITH NO_WAIT
    GO

    ALTER DATABASE DBName SET RECOVERY SIMPLE   --简单模式
    GO

    USE DBName 
    GO

    DBCC SHRINKFILE (N'DBName_log' , 11, TRUNCATEONLY)
    GO

    USE[master]
    GO

    ALTER DATABASE DBName SET RECOVERY FULL WITH NO_WAIT
    GO

    ALTER DATABASE DBName SET RECOVERY FULL  --还原为完全模式
    GO