On Tue, Aug 18, 2015 at 11:23:32PM -0400, Tom Lane wrote: > Craig Ringer <[email protected]> writes: > > On 18 August 2015 at 01:18, David Fetter <[email protected]> wrote: > >> FETCH [in WITH] > > > I'd be a huge fan of this one. I'd love to see FETCH in > > subqueries, too. Currently doing anything like this requires an > > ugly PL/PgSQL wrapper. > > > The cursor would have to be known at plan-time so it could be > > interrogated for its types. > > That's barely the tip of the iceberg of the problems with this idea. > > How many rows would be fetched from the cursor? What row would it > be left on? Whatever answer you give will be wrong from some > perspective, but particularly that of giving the planner any > freedom-of-action to optimize such a query. > > More generally, what would you hope to accomplish with such a > construct that wouldn't be better done by writing the cursor's > underlying query directly in the WITH clause?
So FETCH is not a good candidate for inclusion in WITH, at least until someone comes up with some meaningful definition of what this would mean. Cheers, David. -- David Fetter <[email protected]> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: [email protected] Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
