Random, Unique Number Generation

JoeCrane

OK. I started programming with PHP and MySQL over the past two months and am now weeping over the wasted time spent with ASP... Anyway, I have a decent intranet setup for our company; and, I have setup a billing program to simplify things and allow everyone to see it.

The only problem I am having is, I want a random (not incremental) number generated for each bill; but, the number must also be unique for tax and billing purposes. The only number generation I have found so far simply generates the number without making sure the number is unique. How do I accomplish this feat of logic?

My server use phpMyAdmin 2.3.0 if that makes a difference.

Any help is greatly apreciated.🙂

ultraslacker

I've seen this done with forming a number from timestamp and mac address. It's a solution useful for a clustered database, but otherwise I do not see its advantages over incremental.

Why can't you just use incremental?

nnichols

If you really can't use incremental try something like this -

$error = 1;
// this while clause will loop until it has a unique number
while ($error) {
$num = rand(0, 100000);
if (mysql_num_rows(mysql_query("SELECT * FROM inv_tbl WHERE inv_no=$num")) != 0)
	$error = 1;
else
	$error = 0;
}

It's a bit crude but you should get the idea 😉

ahundiak

The uniqid() should work. Ckech the manual for details.
http://www.php.net/manual/en/function.uniqid.php

You could have more control over the format by generating a random number then checking your billing table to see if it is already used.

iambradn

Best solution is to generate the numebr in your code, and then check with the method nnichols suggested. Generating truly random numbers is much impossible (without having a truly random seed). Also, make sure to set the DB field to be unique, so that you never accidentally insert a duplicate number.