>> I poked around to see if we didn't have some code already for that, and >> soon found that not only do we have such code (equality_ops_are_compatible) >> but actually almost this entire patch duplicates logic that already exists >> in optimizer/util/pathnode.c, to wit create_unique_path's subroutines >> query_is_distinct_for et al. So I'm thinking what this needs to turn into >> is an exercise in refactoring to allow that logic to be used for both >> purposes.
> Well, it seems that might just reduce the patch size a little! > I currently have this half hacked up to use query_is_distinct_for, but I > see there's no code that allows Const's to exist in the join condition. I > had allowed for this in groupinglist_is_unique_on_restrictinfo() and I > tested it worked in a regression test (which now fails). I think to fix > this, all it would take would be to modify query_is_distinct_for to take a > list of Node's rather than a list of column numbers then just add some > logic that skips if it's a Const and checks it as it does now if it's a Var > Would you see a change of this kind a valid refactor for this patch?
I'm a bit skeptical as to whether testing for that case is actually worth any extra complexity. Do you have a compelling use-case? But anyway, if we do want to allow it, why does it take any more than adding a check for Consts to the loops in query_is_distinct_for? It's the targetlist entries where we'd want to allow Consts, not the join conditions.
I don't really have a compelling use-case, but you're right, it's just a Const check in query_is_distinct_for(), it seems simple enough so I've included that in my refactor of the patch to use query_is_distinct_for(). This allows the regression tests all to pass again.
I've included an updated patch and a delta patch.
Now a couple of things to note:
1. The fast path code that exited in join_is_removable() for subquery's when the subquery had no group or distinct clause is now gone. I wasn't too sure that I wanted to assume too much about what query_is_distinct_for may do in the future and I thought if I included some logic in join_is_removable() to fast path, that one day it may fast path wrongly. Perhaps we could protect against this with a small note in query_is_distinct_for().