From: Dean Gibson (DB Administrator) <postgresql4@ultimeth.com>
To: pgsql-sql <pgsql-sql@postgresql.org>
Subject: Re: What does "merge-joinable join conditions" mean ????
Date: Sun, 15 Jan 2006 15:47:56 -0800
Message-ID: <43CADF2C.7010100@ultimeth.com> (raw)
In-Reply-To: <24424.1137368560@sss.pgh.pa.us>
References: <43CAAFA6.6050001@ultimeth.com>
<20060115215448.GA30809@winnie.fuhr.org>
<43CACC78.7090107@ultimeth.com>
<24299.1137367313@sss.pgh.pa.us>
<43CADB44.70309@ultimeth.com>
<24424.1137368560@sss.pgh.pa.us>
On 2006-01-15 15:42, Tom Lane wrote:
>
>> EXPLAIN SELECT count(*) FROM "Extra" FULL JOIN "GeoRestrict" ON
>> callsign ~ pattern WHERE geo_region =
>> 4;
>>
>
> Oh, but that reduces it to a left join, as you can see in the EXPLAIN
> output ---
Yes, I previously noticed that in the EXPLAIN output too.
> any null-extension rows from the right side are going to fail
> the WHERE condition anyway, so the planner simplifies the FULL JOIN to a
> LEFT JOIN. If you'd eliminate the WHERE altogether then the failure
> will come back.
>
>
Tried that, and you are right there as well.
So, given the fact that the right-hand-table is only about 15 rows, do
you think changing the SELECT back to a LEFT JOIN, and then using a
UNION to get the extra right-hand-rows in, is the best work-around?
-- Dean
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To: pgsql-sql@postgresql.org
Cc: postgresql4@ultimeth.com
Subject: Re: What does "merge-joinable join conditions" mean ????
In-Reply-To: <43CADF2C.7010100@ultimeth.com>
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