Message-Id: <6.2.1.2.0.20050922224720.02c365f8@localhost>
Date: Thu, 22 Sep 2005 22:56:47 +0800
To: "Merlin Moncure" <merlin.moncure@rcsonline.com>
From: K C Lau <kclau60@netvigator.com>
Subject: Re: SELECT LIMIT 1 VIEW Performance Issue
Cc: <pgsql-performance@postgresql.org>
In-Reply-To: <6EE64EF3AB31D5448D0007DD34EEB3417DD3FF@Herge.rcsinc.local>
References: <6EE64EF3AB31D5448D0007DD34EEB3417DD3FF@Herge.rcsinc.local>
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At 22:37 05/09/22, Merlin Moncure wrote:

> > >create or replace view VCurPlayer as select * from Player a
> > >where a.AtDate = (select Max(b.AtDate) from Player b where a.PlayerID=
> > >b.PlayerID);
>
>Here is a trick I use sometimes with views, etc.  This may or may not be
>effective to solve your problem but it's worth a shot.  Create one small
>SQL function taking date, etc. and returning the values and define it
>immutable.  Now in-query it is treated like a constant.

We don't use functions as a rule, but I would be glad to give it a try.
I would most appreciate if you could define a sample function and rewrite 
the VCurPlayer view above. Both PlayerID and AtDate are varchar fields.

>Another useful application for this feature is when you have nested
>views (view 1 queries view 2) and you need to filter records based on
>fields from view 2 which are not returned in view 1.  Impossible?
>
>in view 2 add clause where v2.f between  f_min() and f_max(), them being
>immutable functions which can grab filter criteria based on inputs or
>values from a table.
>
>Merlin

Best regards,
KC.