SQL Server 统计某个月周末的天数

---注意:这里统计的周末包括周5,周6,但不包括周日
ALTER FUNCTION [dbo].[GetWeekDaysByMonth]
(
    @Year INT,
    @Month INT,
    @Day INT
)
RETURNS INT
AS
BEGIN
    DECLARE @date DATETIME = DATEFROMPARTS(@Year, @Month, 28);
    DECLARE @weekday INT = 0,
            @weekDays INT = 0,
            @daysCount INT = 0,
            @dayDiff INT = 0;
    SET @daysCount = 32- DAY(DATETIMEFROMPARTS(@Year, @Month, @Day, 1, 1, 1, 1)- DAY(DATETIMEFROMPARTS(@Year, @Month, @Day, 1, 1, 1, 1)) + 32); --月天数
    SET @dayDiff = @daysCount - 28;
    IF @@DATEFIRST = 7
    BEGIN
        SET @weekday = 7 - (8 - DATEPART(WEEKDAY, @date)) % 7;---周几
    END;
    ELSE
    BEGIN
        SET @weekday = DATEPART(WEEKDAY, @date);---周几
    END;
    WHILE @dayDiff > 0
    BEGIN
        IF (@weekday + @dayDiff = 5 OR @weekday + @dayDiff = 6)--判断是否周五,周六  (如果是判断周六周日的天数,条件改为6和7)
            SET @weekDays = @weekDays + 1;
        SET @dayDiff = @dayDiff - 1;
    END;

    --SELECT dbo.GetWeekDaysByMonth56(2018,11,25)
    --SELECT dbo.GetWeekDaysByMonth56(2018,11,26)
    RETURN @weekDays+8;---每个月28天里的周末有8天
END;