---注意:這裡統計的週末包括周5,周6,但不包括週日
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); --月天數
    SET @dayDiff = @daysCount - 28;
    IF @@DATEFIRST = 7
    BEGIN
        SET @weekday = 7 - (8 - DATEPART(WEEKDAY, @date
 
)) % 7;---周幾
    END;
    ELSE
    BEGIN
        SET @weekday = DATEPART(WEEKDAY, @date);---周幾
    END;
    WHILE @dayDiff > 0
    BEGIN
        IF (@weekday + @dayDiff = 5 OR @weekday + @dayDiff = 6)--判斷是否週五,週六  (如果是判斷週六週日的天數,條件改為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;---每個月28天裡的週末有8天
END;