Re: Anti join confusion

On Wed, Feb 26, 2025 at 4:58 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Yeah.  The key problem blocking doing something about it in the
> planner is that at the time we want to do join tree restructuring,
> we haven't yet collected the per-relation data that would allow
> us to know about NOT NULL constraints, nor run expression
> simplification that would be important for detecting all but the
> most basic cases.  Doing either of those things twice seems like
> a nonstarter from a planner-speed viewpoint.  It's possible that
> we could rearrange things to collect catalog data sooner.
> (I'm vaguely imagining that we'd collect that stuff by relation
> OID to begin with, and then when we build RelOptInfos later on
> we could link to the per-rel-OID catalog data.)  Moving expression
> simplification up seems considerably more fraught, but maybe we could
> handle the cases of common interest without having done that.

Oh, this is very helpful! I didn't realize that there were specific
technical obstacles standing in the way of making this happen; I was
assuming it was just a case of nobody having been interested enough to
write the code. That's good to know.

--
Robert Haas
EDB: http://www.enterprisedb.com