On Tue, 8 Sep 2020 at 07:16, Tom Lane <t...@sss.pgh.pa.us> wrote: > > > I'm not sure what I think about Ashutosh's ideas about doing this > somewhere else than eval_const_expressions. I do not buy the argument > that it's interesting to do this separately for each child partition. > Child partitions that have attnotnull constraints different from their > parent's are at best a tiny minority use-case, if indeed we allow them > at all (I tend to think we shouldn't).
I agree about partitions. But, IMO, a child having constraints different from that of a parent is more common in inheritance trees. Another point I raised in my mail was about constraint exclusion. Why aren't these clauses constant-folded by constraint exclusion? Sorry, I haven't looked at the constraint exclusion code myself for this. As a not incidental example, consider > > select ... from t1 left join t2 on (...) where t2.x is not null; > > reduce_outer_joins will realize that the left join can be reduced > to a plain join, whereupon (if t2.x is attnotnull) the WHERE clause > really is constant-true --- and this seems like a poster-child case > for it being useful to optimize away the WHERE clause. But > we won't be able to detect that if we apply the optimization during > eval_const_expressions. So maybe that's a good reason to do it > somewhere later. > +1 -- Best Wishes, Ashutosh
