Robert Haas <robertmhaas@gmail.com> writes:
> You could probably convince me that a merge join is not going to be
> too useful (how often can you want a merge join on the inner side of a
> nested loop?
Why not? As Andrew pointed out, what we're really trying to accomplish
here is consider sub-join plans that are parameterized by a value
obtained from an outer relation. I think we shouldn't artificially
limit what we consider.
But anyway I think we're on the same page here: what we ought to do is
try implementing this scheme without any extra restrictions on what it
considers, and see what the performance is like. We can try to limit
what it considers if it turns out not to work well in the simplest
form.
regards, tom lane