Re: ERROR: failed to build any 4-way joins

Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
> Test suite (as simple as I can produce):

Mmm, sweet :-(. There is only one legal way to form the outer join, but
make_rels_by_joins() doesn't try it because have_relevant_joinclause()
says there is no relevant joinclause ... as indeed there is not, the
"true = true" thing having been optimized away. I guess we need a hack
to treat empty outer join conditions specially.

> Sorry, versions are 8.2 & 8.3. 8.1 works well

Right, not a problem before 8.2 because outer join order was driven by
the syntax instead of by searching for a good join order. Also, you
need at least two base relations on each side of the outer join, else
the "last ditch" case in make_rels_by_joins() finds the join.

regards, tom lane