SQL proc to calculate check digit for 7 and 12 digit upc

Question

I just had to scour the internet for this code yet again so I figured I would put it here so I can find it a little faster the next time and hopefully you found it a little faster too :)

Answer 1

Check this. The code below can check digit in all GTIN's (EAN8, EAN13, EAN14, UPC/A, UPC/E)

CREATE FUNCTION [dbo].[check_digit]
(
    @GTIN VARCHAR(14)
)
RETURNS TINYINT
AS
BEGIN
    DECLARE @Index TINYINT,
            @Multiplier TINYINT,
            @Sum TINYINT,
            @checksum TINYINT,
            @result TINYINT,
            @GTIN_strip VARCHAR(13)

    SELECT  @GTIN_strip = SUBSTRING(@GTIN,1,LEN(@GTIN)-1);

    SELECT  @Index = LEN(@GTIN_strip),
            @Multiplier = 3,
            @Sum = 0

    WHILE @Index > 0
        SELECT  @Sum = @Sum + @Multiplier * CAST(SUBSTRING(@GTIN_strip, @Index, 1) AS TINYINT),
            @Multiplier = 4 - @Multiplier,
            @Index = @Index - 1

    SELECT @checksum = CASE @Sum % 10
            WHEN 0 THEN '0'
            ELSE CAST(10 - @Sum % 10 AS CHAR(1))
        END


    IF (SUBSTRING(@GTIN,LEN(@GTIN),1) = @checksum)
        RETURN 1; /*true*/
        RETURN 0; /*false*/
END