ALTER FUNCTION WEEKDAYS(@DAY VARCHAR)
RETURNS INT
AS BEGIN
    IF(@DAY IS NULL)
    RETURN 0

        DECLARE @OUTPUT INT

        SELECT @OUTPUT=
            CASE WHEN SUBSTRING(@DAY,1,1) = 'M' THEN 1
                 WHEN SUBSTRING(@DAY,1,2) = 'TU' THEN 2
                 WHEN SUBSTRING(@DAY,1,1) = 'W' THEN 3
                 WHEN SUBSTRING(@DAY,1,2) = 'TH' THEN 4
                 WHEN SUBSTRING(@DAY,1,1) = 'F' THEN 5
                 WHEN SUBSTRING(@DAY,1,2) = 'SA' THEN 6
                 WHEN SUBSTRING(@DAY,1,2) = 'SU' THEN 7
            ELSE
                99 END
        RETURN @OUTPUT
    END