Re: WITH RECUSIVE patches 0723

>>>>> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:
[snip spec]

Just out of curiosity, since I don't have a copy of the spec handy, how
does the language for WITH compare to that for views?
Tom> I think this is a "must fix" because of the point about volatileTom> functions --- changing it later will result
inuser-visibleTom> semantics changes, so we have to get it right the first time.
 

I strongly disagree that this should be a blocking issue - the patch
as it stands is an insanely useful feature, allowing many real-world
queries to work which simply were not possible before without
resorting to procedural code or awkward database designs.
Tom> This isn't going to be a particularly simple fix :-(.  The basicTom> implementation clearly ought to be to dump
theresult of theTom> subquery into a tuplestore and then have the upper level readTom> out from that.
 

Which will be a serious pessimization in many common cases if you do
it all the time. Googling for examples of non-recursive WITH queries
shows that it is very widely used for clarity or convenience, in
contexts where you _don't_ want materialization.

Recursive WITH queries that self-join the recursion result seem to be
rare in practice.

-- 
Andrew (irc:RhodiumToad)