Thread: [Fwd: Re: surprising results with random()]

ries van Twisk wrote:

>
> Jessi,
>
> should the function not look like this???
>
> CREATE OR REPLACE VIEW test_view AS
> SELECT
>     CASE
>         WHEN random() < .333333333 THEN '1'
>         WHEN random() < .5 THEN '2'
>         ELSE '3'
>     END AS test_value
>
> FROM client;


actually, I'd think that should be .66666


but... wouldn't    floor(random() * 3.0) + 1  be a simpler way to do this?

John R Pierce <pierce@hogranch.com> writes:
> ries van Twisk wrote:
>> should the function not look like this???
>>
>> CREATE OR REPLACE VIEW test_view AS
>> SELECT
>> CASE
>> WHEN random() < .333333333 THEN '1'
>> WHEN random() < .5 THEN '2'
>> ELSE '3'
>> END AS test_value
>>
>> FROM client;

> actually, I'd think that should be .66666

Nah, ries is correct.  Think of it this way: one-third of the time the
first WHEN succeeds, and you get '1'.  In *half of the remaining cases*,
you want '2', so the second test should be against 0.5.

> but... wouldn't    floor(random() * 3.0) + 1  be a simpler way to do this?

Agreed...

            regards, tom lane