Re: Poor performance using CTE

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: Claudio Freire <klaussfreire(at)gmail(dot)com>
Cc: David Greco <David_Greco(at)harte-hanks(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Poor performance using CTE
Date: 2012-11-20 15:23:50
Message-ID: CAHyXU0z4oUss50vhH_wGZ-HERQe9wCMSf1nMTGNddXeCoKvVVA@mail.gmail.com
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On Tue, Nov 20, 2012 at 9:10 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> On Tue, Nov 20, 2012 at 12:04 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>> The problem here is very clear. Oracle is optimizing through the CTE.
>> PostgreSQL does not do this by design -- CTE's are used as a forced
>> materialization step.
>
> While I love that design (it lets me solve lots of problems for huge
> queries), wouldn't pushing constraints into the CTE be a rather safe
> optimization?

sure, or rewrite query as classic join.

merlin

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