On 2009-05-03, Erik Jones <ejones@xxxxxxxxxxxxxx> wrote: >> What I'm looking for is a function that, given an input within a >> constrained range (say, a 32 bit integer) produces a different output >> within the same range. For any given input, the output should be the >> same each time, and for any given output there should only be one >> input >> that results in that output. > > I think you drop the idea of a repeatable mapping you may have some > success with the Knuth (aka Fisher-Yates) shuffle algorithm: http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle > Why does anything need to be repeatable when you only need to make > sure that each number is only generated once? That means storing a long list of numbers and doing queries similar to the following to get ne next value for the sequence. select id from idtable order by id limit 1 offset random(0, (select count (*) from idtable) a ramdom-looking 1:1 mapping is potentially much more efficient. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
