Generating Random Numbers as primary key In PHP / Mysql

What is the best way to generate alphanumeric random number to 8 digit in php which is case sensitive? I want to use this unique number to be stored in mysql data base and make开发者_如何学C it a primary key.

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Never use a random key as primary key. Primary keys need to be unique in most cases and random numbers are not.

E.g.

1 1 1 1 1 1 0 1 

is also a valid output of a 8 digit random number generator.

You should use auto-increment fields or generators instead to make sure that your primary key is really unique.

If you want to have a identifier which is likely to be unique and some sort of random try to use mysql facilities like: http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_uuid

A caveat might be to reiterate inserts multiple times.

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I suppose you could trim a hash (md5() or sha1() etc.) of a field in the item to 8 characters- although you might end up with a collision.

Why not make the primary key field AUTOINCREMENT? Why does it need to be 8 alphanumeric characters?

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You could probably use the uniqid function.

But make sure you really want to do that. An AUTOINCREMENT column might be a better solution.

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Not random, but if you don't want your IDs to be sequential then perhaps you could encrypt them in some way. See the following question on the same topic: Simple integer encryption