Generate unique random alphanumeric characters that are 7 characters long

Question

It need not be meaningful words - more like random password generation, but the catch is - they should be unique. I will be using this for some kind of package / product cod

Answer 1

Here is something that looks random and should be unique and have 7 chars for the times to come:

echo base_convert(intval(microtime(true) * 10000), 10, 36);

Or for a little more randomness and less uniqueness (between 1000 and 10000 per second):

echo base_convert(mt_rand(1, 9) . intval(microtime(true) * 1000), 10, 36);

Or (uniqueness between 100 and 10000 per second) - this is probably the best option:

echo base_convert(mt_rand(10, 99) . intval(microtime(true) * 100), 10, 36);

Or (uniqueness between 10 and 10000 per second):

echo base_convert(mt_rand(100, 999) . intval(microtime(true) * 10), 10, 36);

You get the idea.