By definition, it is equivalent to:
SELECT t1.id, t2.url FROM referral_temp t2 LEFT /*OUTER*/ JOIN d_referral t1
ON t2.url = t1.referral_raw_url
union all
SELECT null, url FROM referral_temp WHERE url is null
ORDER BY 1;
/Aaron
----- Original Message -----
From: "Joe Conway" <mail@joeconway.com>
To: "Sean Shanny" <shannyconsulting@earthlink.net>
Cc: <pgsql-performance@postgresql.org>
Sent: Friday, April 23, 2004 12:38 AM
Subject: Re: [PERFORM] Looking for ideas on how to speed up warehouse
loading
> Sean Shanny wrote:
> > explain analyze SELECT t1.id, t2.url FROM referral_temp t2 LEFT OUTER
> > JOIN d_referral t1 ON t2.url = t1.referral_raw_url ORDER BY t1.id;
>
> > What I would like to know is if there are better ways to do the join? I
> > need to get all the rows back from the referral_temp table as they are
> > used for assigning FK's for the fact table later in processing. When I
> > iterate over the values that I get back those with t1.id = null I assign
> > a new FK and push both into the d_referral table as new entries as well
> > as a text file for later use. The matching records are written to a
> > text file for later use.
>
> Would something like this work any better (without disabling index scans):
>
> SELECT t1.id, t2.url
> FROM referral_temp t2, d_referral t1
> WHERE t1.referral_raw_url = t2.url;
>
> <process rows with a match>
>
> SELECT t1.id, t2.url
> FROM referral_temp t2
> WHERE NOT EXISTS
> (select 1 FROM d_referral t1 WHERE t1.referral_raw_url = t2.url);
>
> <process rows without a match>
>
> ?
>
> Joe
>
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