The following is the obvious PGSQL code, you'd obviously need something
else to stop duplicates.
SELECT array_to_string(array((
SELECT SUBSTRING('abcdefghjklmnpqrstuvwxyz23456789'
FROM mod((random()*32)::int, 32)+1 FOR 1)
FROM generate_series(1,5))),'');
As this only generates five characters and each character can be one of
32 values, you've got about 33554432 choices and you'd have a 50% chance
of getting a duplicate after 7240 values. This assumes I wrote the
above code correctly. It's also not amazing because PG's random number
generator is defined to return a value between 0 and 1 inclusive, it's
generally much more useful if it runs from 0 to less than 1 and would
mean that I wouldn't need the "mod" above and would remove the (slight)
biasing towards choosing 'a'.
That does actually work! I'm not sure why you're saying that there's a 50% chance of duplication after 7240 values though. With 33 million combinations, I would have thought that duplications would become equally likely at the 16,777,216 mark.
I hadn't thought of coding it the way you did, which is an interesting way of approaching it!
Thom