From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <riguo@pivotal.io>
cc: Arne Roland <A.Roland@index.de>,
        "pgsql-hackers@lists.postgresql.org"
 <pgsql-hackers@lists.postgresql.org>
Subject: Re: Partial join
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 <CAN_9JTxQtJr2RHLKAfDCJoZFF+qsUMAF5JF+BVyAVcmcC2kSQA@mail.gmail.com>
References: <9dc03e949e9b4327a0d074da9ab44318@index.de>
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Comments: In-reply-to Richard Guo <riguo@pivotal.io>
	message dated "Thu, 01 Aug 2019 19:14:44 +0800"
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Date: Thu, 01 Aug 2019 10:14:54 -0400
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Richard Guo <riguo@pivotal.io> writes:
> For the third query,  a rough investigation shows that, the qual 'sl =
> 5' and 'sc.sl = sg.sl' will form an equivalence class and generate two
> implied equalities: 'sc.sl = 5' and 'sg.sl = 5', which can be pushed
> down to the base rels. One consequence of the deduction is when
> constructing restrict lists for the joinrel, we lose the original
> restrict 'sc.sl = sg.sl', and this would fail the check
> have_partkey_equi_join(), which checks if there exists an equi-join
> condition for each pair of partition keys. As a result, this joinrel
> would not be considered as an input to further partitionwise joins.

> We need to fix this.

Uh ... why?  The pushed-down restrictions should result in pruning
away any prunable partitions at the scan level, leaving nothing for
the partitionwise join code to do.

			regards, tom lane