Question

Question:

I need to COMPARE if a string is a MD5 Hash in SQL.

I found this PHP-function:

function isValidMd5($md5)
{
    return !empty($md5) && preg_match('/^[a-f0-9]{32}$/', $md5);
}

Since SQL lacks the {32} syntax, I just duplicate [a-f0-9] 32 times:

IF '200ceb26807d6bf99fd6f4f0d1ca54d4' LIKE '[a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9]' 
BEGIN
    PRINT 'YES'
END
ELSE
BEGIN
    PRINT 'NO'
END 

However, to avoid a possible collision with a username consisting of 32 [a-f], however unlikely, I want to do the like comparison uppercase.

But if for testing purposes I do:

IF 'E' COLLATE Latin1_General_CS_AS  LIKE ('[a-f0-9]' COLLATE Latin1_General_CS_AS )
BEGIN
    PRINT 'yes'
END
ELSE
BEGIN
    PRINT 'no'
END 

I get yes, and not no.
However COLLATE Latin1_General_CS_AS should make it case-sensitive…

How can a make the LIKE in this IF case-sensitive ?

Answer 1

Better to invert the check and make it simpler to maintain by checking for any single thing that will make it fail. This means you don’t have to repeat [0-9a-f] 32 times in the code.

IF LEN(@myValue) <> 32 OR LOWER(@myValue) LIKE '%[^0-9a-f]%' 
BEGIN
   -- No it isn't
END ELSE BEGIN
   -- Yes it is
END

i.e., if it’s not 32 chars OR it contains a character outside the hexadecimal set then it fails.