On Wed, Jun 8, 2016 at 12:25 PM, Amit Langote <langote_amit...@lab.ntt.co.jp
> wrote:

> On 2016/06/08 14:13, Ashutosh Bapat wrote:
> > On Tue, Jun 7, 2016 at 6:19 PM, Amit Langote wrote:
> >> On Tue, Jun 7, 2016 at 7:47 PM, Ashutosh Bapat wrote:
> >>> Looks good to me. If we add a column from the outer relation, the
> >> "NULL"ness
> >>> of inner column would be more clear. May be we should tweak the query
> to
> >>> produce few more rows, some with non-NULL columns from both the
> >> relations.
> >>> Also add a note to the comment in the test mentioning that such a join
> >> won't
> >>> be pushed down for a reader to understand the EXPLAIN output. Also, you
> >>> might want to move that test, closer to other un-pushability tests.
> >>
> >> Done in the attached.  Please check if my comment explains the reason
> >> of push-down failure correctly.
> >
> > On further thought, I think we need to restrict the join pushdown only
> for
> > outer joins. Only those joins can produce NULL rows. If we go with that
> > change, we will need my changes as well and a testcase with inner join.
> I think the added test in foreign_join_ok() would restrict only the outer
> joins from being pushed down (and further, only those with placeholdervars
> in their targetlist being referred to above their level).  Do you have any
> query handy as example where unintended push-down failure occurs?
Right, PHVs are created in case of outer joins. So, for an inner join the
list will not have anything in there for it.

Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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