Re: PostgreSQL Gotchas

On 10/7/05, Michael Fuhr <mike(at)fuhr(dot)org> wrote:
> On Thu, Oct 06, 2005 at 05:47:36PM -0500, Jeffrey Melloy wrote:
> > The only thing I could see actually being an issue is the random() one
> > and add missing from. The rest are trivial. The random() thing is
> > interesting, esoteric, and probably has never been a problem in a real
> > situation. (Or has exactly once, when he wrote that gotcha)
>
> The random() issue has a workaround that the gotchas page doesn't
> mention:
>
> SELECT id, is_true
> FROM (SELECT id, RANDOM() < 0.5 AS is_true FROM some_table OFFSET 0) AS t_tmp
> WHERE is_true;
>
> Tom Lane brought up the OFFSET 0 trick a couple of days ago in the
> "Avoiding evaluating functions twice" thread:
>
> http://archives.postgresql.org/pgsql-general/2005-10/msg00107.php

Thanks, I've updated the list.

I'd like to take the opportunity to point out that following the
original, unexpected "success" of the MySQL gotchas list, I created
one for PostgreSQL for the sake of "balance". Though I'm really having
to scrape the barrel for material ;-).

The MySQL list is a little outdated; I'm going through it with updates
for version 5.

Ian Barwick