Re: WITH RECUSIVE patches 0723

Martijn van Oosterhout <kleptog@svana.org> writes:
> Since the problem is using the result of a WITH clause more than once,
> would it be sufficient to simply detect that case and bail? You don't
> want materialisation is most cases, there's just a few where it is
> needed.

Really?  I tried googling to see what other people thought that the
WITH clause was for, and the first relevant hit I got was this one:
http://www.oracle-developer.net/display.php?id=212
which certainly treats it as a key part of the feature.

My thought is that we could optimize away materialization in cases where
we can tell it's not needed (no volatile functions and/or no multiple
scans of the subquery).  But not being able to do it means we've
implemented the feature incorrectly.
        regards, tom lane