10

I am attempting to hash a string to a 64-bit value (bigint) in MySQL. I am aware of the MD5() function, which returns a 128-bit hash as a binary string. I'd be happy to just take the bottom or top 64 bits of this result. However, I cannot figure out how to get from a binary string type to a numeric type of any sort. Any pointers?

Sean Owen
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3 Answers3

16

Use the CONV() function to convert the MD5 hash from base 16 to base 10 and CAST to convert it to a number:

select cast(conv(substring(md5(id), 1, 16), 16, 10) as unsigned integer) from SomeTable;
Ken Keenan
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    Nice, that's what I'm looking for. I think I don't need the cast, or want to cast to bigint, but the conv() function was really what I was missing. – Sean Owen Aug 11 '09 at 11:26
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    One final note. I was then accessing this numeric value as a long in Java. Java integer types are signed, and the result of conv() is always positive, which means it overflows in some cases. For those using this as a signed long, you do need the cast, and casting to 'signed' does the trick. – Sean Owen Aug 25 '09 at 09:51
2
CREATE FUNCTION dbo.HexStrToVarBinary(@hexstr varchar(8000))
RETURNS varbinary(8000)
AS
BEGIN 
    DECLARE @hex char(1), @i int, @place bigint, @a bigint
    SET @i = LEN(@hexstr) 

    set @place = convert(bigint,1)
    SET @a = convert(bigint, 0)

    WHILE (@i > 0 AND (substring(@hexstr, @i, 1) like '[0-9A-Fa-f]')) 
     BEGIN 
        SET @hex = SUBSTRING(@hexstr, @i, 1) 
        SET @a = @a + 
    convert(bigint, CASE WHEN @hex LIKE '[0-9]' 
         THEN CAST(@hex as int) 
         ELSE CAST(ASCII(UPPER(@hex))-55 as int) end * @place)
    set @place = @place * convert(bigint,16)
        SET @i = @i - 1

     END 

    RETURN convert(varbinary(8000),@a)
END
GO

Source

Max
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2

You could also use CRC32 function that returns 32-bit unsigned value.

SELECT CRC32(id) from SomeTable;

Documentation

Łukasz Żarczyński
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