(2018/01/16 12:00), Etsuro Fujita wrote:
(2018/01/16 11:17), Tom Lane wrote:
Etsuro Fujita<fujita.ets...@lab.ntt.co.jp> writes:
(2018/01/16 1:47), Robert Haas wrote:
Hmm, I was thinking that bar and baz wouldn't be constrained to return
just one tuple in that case, but I'm wrong: there would just be one
tuple per relation in that case. However, that would also be true for
a full join, wouldn't it?
Consider:
postgres=# create table bar (a int, b text);
postgres=# create table baz (a int, b text);
postgres=# insert into bar values (1, 'bar');
postgres=# insert into baz values (2, 'baz');
postgres=# select * from bar full join baz on bar.a = baz.a;
a | b | a | b
---+-----+---+-----
1 | bar | |
| | 2 | baz
(2 rows)
Both relations have one tuple, but the full join produces two join
tuples. I think it would be possible that something like this happens
when executing a local join plan for a foreign join that performs a full
join remotely.
Doesn't really matter though, does it? Each of those join rows will
be processed as a separate EPQ event.
I assume that such a local join plan is executed as part of a FOR UPDATE
query like the one shown by Robert (the bar/baz foreign join part in
that query), so I am thinking that those join rows will be processed as
a single event.
I realized I am wrong; the local join execution plan would never produce
multiple tuples in a single event.
Best regards,
Etsuro Fujita
