Question

i want to generate a sequence of unique random numbers in the range of 00000001 to 99999999.

So the first one might be 00001010, the second 40002928 etc.

The easy way is to generate a random number and store it in the database, and every next time do it again and check in the database if the number already exists and if so, generate a new one, check it again, etc.
But that doesn’t look right, i could be regenerating a number maybe 100 times if the number of generated items gets large.

Is there a smarter way?

EDIT
as allways i forgot to say WHY i wanted this, and it will probably make things clearer and maybe get an alternative, and it is:
we want to generate an ordernumber for a booking, so we could just use 000001, 000002 etc. But we don’t want to give the competitors a clue of how much orders are created (because it’s not a high volume market, and we don’t want them to know if we are on order 30 after 2 months or at order 100. So we want to have an order number which is random (yet unique)

Answer 1

You could build a table with all the possible numbers in it, give the record a ‘used’ field.

1. Select all records that have not been ‘used’
2. Pick a random number (r) between 1 and record count
3. Take record number r
4. Get your ‘random value’ from the record
5. Set the ‘used’ flag and update the db.

That should be more efficient than picking random numbers, querying the database and repeat until not found as that’s just begging for an eternity for the last few values.