Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Aug 24, 2009 at 9:31 PM, Josh Berkus<josh@agliodbs.com> wrote:
>> What I don't get is why this is such a usability issue. �Subqueries in
>> DELETE FROM work perfectly well, and provide more flexibility than most
>> users know what to do with.
> It's both a usability issue and a performance issue.
On the usability front: if we were to take the position Josh advocates,
we should never have added FROM/USING to UPDATE/DELETE at all ... but
since we did, I think we should try to make it as flexible as the
corresponding feature in other DBMSes.
On the performance front: yeah, you can recast most joins as subqueries,
but you tend to end up with the equivalent of a nestloop plan. Works
okay for small numbers of rows, scales horribly.
regards, tom lane