请教一个简单的语法问题，关于case

Question

我测试了下：
select case  when isdate('2005'+'02'+'29')=1 then DATENAME(weekday,cast('2005'+'02'+'29' as datetime))
 else '0' end--报错：从 char 数据类型到 datetime 数据类型的转换导致 datetime 值越界。
这可能是因为在语句执行前，编译时，会先把“'2005'+'02'+'29' ”转换成日期，因为没这个日期，所以会先报错了。select case  when isdate('2005'+'02'+'28')=1 then DATENAME(weekday,cast('2005'+'02'+'28' as datetime))
 else '0' end
--成功：星期一

Answer 1

恩，但是得作判断啊，因为我前面是要有
delcare @year char(4),@month char(2),@month2 char(2)的
也就是说得遍历整个月，必须要作判断，否则直接写就更加错了
正确的情况就不用说了，就是这种不存在的情况才做的判断，但是判断似乎没有作用，各位仁兄有何高见？

Answer 2

这也就是加“isdate()”的目的阿

Answer 3

to: xingfu2000(幸福)
语句本身没问题，但在编译的时候会因为日期不存在而产生异常，你最好控制一下别传个不存在的日期给他，因为当转换的时候是肯定会出错的

Answer 4

先判定该月有多少天吧。。
select day(dateadd(dd,-1,'2005-03-01'))
取上与的最大天数就是下月的一号减一天。

Answer 5

declare @year char(4),@year2 char(4),@month char(2),@month2 char(2)
set @year='2004'
set @year2='2004'
set @month='09'
set @month2='10'
SET DATEFIRST 1
select @year,@year2,@month,@month2
       ,datepart(weekday,convert(datetime,@year+@month+'21'))
       ,datepart(weekday,convert(datetime,@year+@month+'22'))
       ,datepart(weekday,convert(datetime,@year+@month+'23'))
       ,datepart(weekday,convert(datetime,@year+@month+'24'))
       ,datepart(weekday,convert(datetime,@year+@month+'25'))
       ,datepart(weekday,convert(datetime,@year+@month+'26'))
       ,datepart(weekday,convert(datetime,@year+@month+'27'))
       ,datepart(weekday,convert(datetime,@year+@month+'28'))
       ,case isdate(@year+@month+'29') when 1 
then
 case when (datepart(weekday,convert(datetime,@year+@month+'28'))+1)>7
 then convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))-6)
 else convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))+1)
        end
else ''
end
       ,case isdate(@year+@month+'30') when 1
 then
 case when (datepart(weekday,convert(datetime,@year+@month+'28'))+2)>7
 then convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))-5)
 else convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))+2)
      end
 else ''
 end
       ,case isdate(@year+@month+'31') when 1 
then
 case when (datepart(weekday,convert(datetime,@year+@month+'28'))+3)>7
 then convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))-4)
 else convert(char(1),datepart(weekday,convert(datetime,@year+@month+'28'))+3)
        end
else ''
end
       ,datepart(weekday,convert(datetime,@year2+@month2+'01'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'02'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'03'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'04'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'05'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'06'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'07'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'08'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'09'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'10'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'11'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'12'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'13'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'14'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'15'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'16'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'17'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'18'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'19'))
       ,datepart(weekday,convert(datetime,@year2+@month2+'20'))