(讨论)计算当月的星期日天数有关问题

(讨论)计算当月的星期日天数问题
--功能就是计算某一月份的星期日天数、应该出勤天数

--应该出勤天数=月份天数-星期日天数
--大家帮忙看看，哪里可以优化，找个最简单的方法来解决，谢谢了。
CREATE   FUNCTION   FUN_CoutDaysOfMonth
(@YearMonth   nvarchar(7) --月份
,@CountType   int --0   整月天数;   1星期日天数;   2应该出勤天数
)
RETURNS   int
AS    
BEGIN  
    DECLARE  
@BeginDate   datetime
,@EndDate   datetime
,@Return   int
,@SumSunDay   int
SET   @BeginDate=@YearMonth+ '-01 '
SET   @EndDate=DATEADD(Day,-1,DATEADD(month,1,@BeginDate))
SET   @Return=DATEDIFF(day,@BeginDate,@EndDate)+1
IF(@CountType=0)   RETURN   @Return
SET   @SumSunDay=(SELECT   SUM(CASE   ISDATE(@YearMonth+ '- '+D)   WHEN   1   THEN   CASE   RIGHT(DATENAME(Weekday,@YearMonth+ '- '+D),1)   WHEN   '日 '   THEN   1   ELSE   0   END     ELSE   0   END)
FROM   (
SELECT   '01 '   D   UNION   ALL
SELECT   '02 '   UNION   ALL
SELECT   '03 '   UNION   ALL
SELECT   '04 '   UNION   ALL
SELECT   '05 '   UNION   ALL
SELECT   '06 '   UNION   ALL
SELECT   '07 '   UNION   ALL
SELECT   '08 '   UNION   ALL
SELECT   '09 '   UNION   ALL
SELECT   '10 '   UNION   ALL
SELECT   '11 '   UNION   ALL
SELECT   '12 '   UNION   ALL
SELECT   '13 '   UNION   ALL
SELECT   '14 '   UNION   ALL
SELECT   '15 '   UNION   ALL
SELECT   '16 '   UNION   ALL
SELECT   '17 '   UNION   ALL
SELECT   '18 '   UNION   ALL
SELECT   '19 '   UNION   ALL
SELECT   '20 '   UNION   ALL
SELECT   '21 '   UNION   ALL
SELECT   '22 '   UNION   ALL
SELECT   '23 '   UNION   ALL
SELECT   '24 '   UNION   ALL
SELECT   '25 '   UNION   ALL
SELECT   '26 '   UNION   ALL
SELECT   '27 '   UNION   ALL
SELECT   '28 '   UNION   ALL
SELECT   '29 '   UNION   ALL
SELECT   '30 '   UNION   ALL
SELECT   '31 '  
)   A
)
IF(@CountType=1)   RETURN   @SumSunDay
IF(@CountType=2)   RETURN   @Return-@SumSunDay
RETURN   @Return
END


------解决方案--------------------
像LZ這樣運算的...要是碰到個國慶節,勞動節,春節之類的,還不要更麻煩
------解决方案--------------------
乳沟兄好有经验哦...
------解决方案--------------------
慚愧慚愧...偶是CSDN學到的^^