mysql random generated value

Question

I need to generate a random alpha/numeric to give to users that they come to the site to enter. I dont' know much about random numbers and such, I know there are seeding issues and such, but I'm not sure what they are.

So, I used this:

select substrING(md5(concat_ws('-',md5(username_usr), MD5(zip_usr), MD5(id_usr), MD5(created_usr))),-12) from users_usr

Is this safe? I used concat_ws because sometimes zip is null, but the others never are.

And yes, I know this is kinda short, but 1. They have to enter the last 4 of their social, 2. It's 1 time use, 3. There's no private data displayed back in the application and 4. I may use captcha, but since there's no private data, thats probably overkill.

THanks

Anonymous · Accepted Answer · 2009-02-12 15:25:17Z

5

Maybe using the Universal Unique Identifier would suffice? Just to keep it simple?

answered Feb 12, 2009 at 15:25

Anonymous

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soulmerge · Accepted Answer · 2009-02-12 15:29:16Z

4

If you need a random alphanumeric value, why are you using so many variables? Something like the following should be perfectly enough:

md5(rand())
--Flavor: MySql

answered Feb 12, 2009 at 15:29

soulmerge

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1 Comment

wdog Over a year ago

As documentation says: Although UUID() values are intended to be unique, they are not necessarily unguessable or unpredictable. If unpredictability is required, UUID values should be generated some other way.... this solution is far better in my opinion you can do something like update tablename set uuid = md5(rand()+id) ;

dannysauer · Accepted Answer · 2009-02-12 15:44:41Z

It'd help to know the purpose of the "random" string. This isn't random - it's repeatable - and fairly easily repeatable, at that. You're not exposing any sensitive information in a way that's easily reversible, but I'm guessing you're really looking for a way to generate a UUID (univeraslly unique ID). Not coincidentally, recent MySQL versions have a function called UUID.

http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_uuid

That might better solve the problem you're trying to address. If you really want a random number (which can definitely have collisions, by the way) for some reason, don't worry about seeding. If you don't specify a seed, it'll self-seed in a way that's probably better than a fixed seen anyway. You'd then map that random number (or a series of random numbers) to a character (possibly by casting the integer to a char), and repeat that until you have a string of chars long enough. But it bears repeating that a random number is not a guaranteed unique number...

chaos · Accepted Answer · 2010-04-14 05:43:44Z

0

Someone in the deleted duplicate of this question suggested using UUID(), which I think is a good idea. I don't think there's anything greatly wrong with using MD5(RAND()) either.

You'd have to store those, of course, which you don't have to do with your example.

edited Apr 14, 2010 at 5:43

answered Feb 12, 2009 at 15:30

chaos

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Uday Hiwarale · Accepted Answer · 2013-10-19 18:32:30Z

0

>>SELECT md5(RAND()+CURRENT_TIMESTAMP())

answered Oct 19, 2013 at 18:32

Uday Hiwarale

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