pá 24. 7. 2020 v 19:46 odesílatel Tom Lane <t...@sss.pgh.pa.us> napsal:
> Andres Freund <and...@anarazel.de> writes: > > Wouldn't the rule that I proposed earlier, namely that sub-expressions > > that involve only "proper" constants continue to get evaluated even > > within CASE, largely address that? > > The more I think about that the less I like it. It'd make the behavior > even harder to reason about than it is now, and it doesn't fix the issue > for subquery pullup cases. > > Basically this seems like a whole lot of thrashing to try to preserve > all the details of a behavior that is kind of accidental to begin with. > The argument that it's a performance issue seems hypothetical too, > rather than founded on any observed results. > > BTW, to the extent that there is a performance issue, we could perhaps > fix it if we resurrected the "cache stable subexpressions" patch that > was kicking around a year or two ago. That'd give us both > at-most-one-evaluation and no-evaluation-until-necessary behaviors, > if we made sure to apply it to stable CASE arms. > +1 regards Pavel > regards, tom lane > > >
