Re: Equivalence Classes when using IN

From: Kim Rose Carlsen <krc(at)hiper(dot)dk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Equivalence Classes when using IN
Date: 2017-10-11 19:37:50
Message-ID: 00313177-8506-43BC-9F6B-2C19F0E5A98B@hiper.dk
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> Yeah. The ORDER BY creates a partial optimization fence, preventing
> any such plan from being considered.
>>

I can see in the general case it semanticly means different things If you allow the WHERE to pass through ORDER BY.

A special case can be allowed for WHERE to pass the ORDER BY if the column is part of DISTINCT ON.

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