Re: [HACKERS] Partition-wise join for join between (declaratively)partitioned tables

On Wed, Apr 26, 2017 at 12:41 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> So this is about a cross-type join,
>> not multiple types within a single partitioning hierarchy, as you
>> might also gather from the subject line of this thread.
>
> OK, but I still don't understand why any type conversion is needed
> in such a case.  The existing join estimators don't try to do that,
> for the good and sufficient reasons you and I have already mentioned.
> They just apply the given cross-type join operator, and whatever
> cross-type selectivity estimator might be associated with it, and
> possibly other cross-type operators obtained from the same btree
> opfamily.
>
> The minute you get into trying to do any type conversion that is not
> mandated by the semantics of the query as written, you're going to
> have problems.

There is no daylight whatsoever between us on this issue.

-- 
Robert Haas
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