SQL語句中另類IF--ELSE

declare   @Conditions   varchar ( 10 )
set   @Conditions = ''
select   *   from  TabelA 
   where  (( @Conditions <> ''   AND  colName = @Conditions ) 
         or  ( @Conditions = ''   AND  colName <> @Conditions ))
-- 改進版
select   *   from  TabelA 
   where  (colName = @Conditions   or   @Conditions = '' )

-- 查找表TabelA中記錄,如果變量@Conditions為空,則條件為colName<>@Conditions,否則根據@Conditions過濾