sql-计算每个月星期几有几天

--建立函数计算星期
create function w_count(
@ym varchar(6)  --月份
,@dw varchar(8))--星期几
returns int
as
begin
declare @count_day int = 0
declare @b datetime = cast(@ym + '' as datetime)
declare @e datetime = cast(dateadd(dd,-1,dateadd(MM,1,@ym + '')) as datetime)
    while(@b <= @e)
    begin
        if(DATENAME(DW,@b) = @dw)
        begin
            set @count_day = @count_day + 1
        end
        set @b = DATEADD(DD,1,@b)
    end
return(@count_day)
end
go

--测试
select dbo.w_count('','星期六')