--指定月份天数
declare @m varchar(7)
set @m='2012-08'
select datediff(day,@m+'-01',dateadd(month,1,@m+'-01'))

--指定月份工作天数
declare @dt datetime,@dt2 datetime,@i int
set @dt=convert(datetime,@m+'-01')
set @dt2=dateadd(month,1,@dt)
while @dt<@dt2
begin
    if datepart(weekday,@dt)<>1 and datepart(weekday,@dt)<>6
        set @i=isnull(@i,0)+1
    set @dt=dateadd(day,1,@dt)    
end
select @i

------解决方案--------------------
SQL code
create  function getWorkDays( @year int , @month int )
returns int as 
begin 
    declare @CountDay int  
    declare @temptime datetime
    set @CountDay = 0 
    set @temptime = convert(varchar,@year) + '-'+ convert(varchar,@month) + '-01' 
     while(MONTH(@temptime) = @month)
     begin
         if DATEPART(weekday,@temptime) <>1 and DATEPART(weekday,@temptime)<>7
          begin
             set @CountDay = @CountDay + 1 
           End
        set @temptime = DATEADD(day,1,@temptime)
     end
    return @CountDay
end 

--调用
select dbo.getWorkDays(2009,7)