数据库备份和删除旧文件 存储过程

CREATE proc [dbo].[PROC_BACKUPJOINTOWN]
as
declare @sql nvarchar(4000),@return_value int,@par nvarchar(1000)--D:\testback\JOINTOWN20130916.bak
if not exists(
 select * from master..sysdatabases
  where name='JOINTOWN'
  )
BEGIN--数据库不存在
 return
end
else
BEGIN
  SELECT @par=CONVERT(VARCHAR(8), GETDATE(), 112) ;
  select @sql='BACKUP DATABASE JOINTOWN to disk=''D:\testback\JOINTOWN'+@par+'.bak''' ;
  EXECUTE @return_value= sp_executesql @sql ;
  SELECT @return_value;
  IF @return_value=0
  BEGIN
    EXEC sp_configure 'show advanced options' , 1;
    RECONFIGURE;
    EXEC sp_configure 'xp_cmdshell' ,1;
    RECONFIGURE;
   SELECT @par=CONVERT(VARCHAR(8), GETDATE()-1, 112) ;
    select @sql='del D:\testback\JOINTOWN'+ @par+'.bak';
    EXEC master..xp_cmdshell @sql,NO_OUTPUT;
  END
  ELSE
  BEGIN
   RETURN
  END
END