Over here ->
http://www.postgresql.org/message-id/6351.1404663...@sss.pgh.pa.us Tom
noted that create_unique_path did not check for set returning functions.

Tom Wrote:
> I notice that create_unique_path is not paying attention to the question
> of whether the subselect's tlist contains SRFs or volatile functions.
> It's possible that that's a pre-existing bug.

I looked at this a bit and I can confirm that it does not behave as it
should do. Take the following as an example:

create table x (id int primary key);
create table y (n int not null);

insert into x values(1);
insert into y values(1);

select * from x where (id,id) in(select n,generate_series(1,2) / 10 + 1 g
from y);
(1 row)

select * from x where (id,id) in(select n,generate_series(1,2) / 10 + 1 g
from y group by n);
(2 rows)

The 2nd query does group by n, so query_is_distinct_for returns true,
therefore the outer query think's it's ok to perform an INNER JOIN rather
than a SEMI join, which is this case produces an extra record.

I think we should probably include the logic to test for set returning
functions into query_is_distinct_for.

The attached fixes the problem.


David Rowley

Attachment: query_is_distinct_for_fix.patch
Description: Binary data

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