On Sat, Nov 16, 2002 at 15:18:58 -0500, Tom Lane <[EMAIL PROTECTED]> wrote: > Neil Conway <[EMAIL PROTECTED]> writes: > > Bruce Momjian <[EMAIL PROTECTED]> writes: > >> "Random" randomly fails. It is OK. > > > So why is it a regression test, then? > > It's hard to see how you could test random() in a completely > deterministic fashion ...
You could use the floor function and check that function call works and that returned values are in the range >= 0 and < 1 (the description just says between but this is the normal range). You could also do a couple of selects that compare random's output to each other to see if it is generating a constant. The odds of this happening by chance are very small. If you tie a couple of these together you should be able to reduce the chances to whatever you think is safe. The odds of the following returning true should be less than the chances of a hardware hiccup: select random() = random() and random() = random(); The following should always return 0 (assuming I am right about random being strictly less than 1): select floor(random()); You can probably come up with other tricks. For example for a large sample you should be able to put a bound on the average for which the probability of the average being outside that bound is comparable to the test for random returning constant values. The variance is something else that could be tested this way. ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/users-lounge/docs/faq.html
