On 10/7/05, Michael Fuhr <mike@xxxxxxxx> 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 The MySQL list is a little outdated; I'm going through it with updates for version 5.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 ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
