On Aug 16, 2009, at 5:07 AM, Thom Brown wrote:
Does anyone know a way to generate a random and unique lowercase
alphanumeric ID (preferably without using 0, 1, o or i to prevent
problems with users manually typing the ID) using SQL without
resorting to a prerendered table or using GUIDs.
For example, if I were to ask for an ID of 5 characters, something
like the following would be returned:
hn21o
8sp2j
9wwun
m7z02
Notice that I don't mean hexadecimal values either. This would
preferrably not resort to trying to generate the ID, then checking
for a clash, and if there is one, do it again, although that could
do as I can't think of how the ideal solution of a ID hashing
algorithm would be possible.
One way is to use a LFSR (linear feedback shift register function). I
haven't used one in a long time but I recall generating pseudo random
numbers that are guaranteed not to repeat after billions of
iterations. It's very fast as well. Then translate the resulting
integer into the character sequence of your choosing. Here is a
reference: http://en.wikipedia.org/wiki/Linear_feedback_shift_register
Bob Gobeille
Hewlett Packard
Open Source Program Office
(and http://fossology.org)
