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Re: foreign key is it a real key

From: Andreas Kretschmer <akretschmer(at)spamfence(dot)net>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: foreign key is it a real key
Date: 2012-02-13 15:50:47
Message-ID: 20120213155047.GA25335@tux (view raw or flat)
Thread:
Lists: pgsql-sql
John Fabiani <johnf(at)jfcomputer(dot)com> wrote:

> Hi,
> I have read a few articles and I'm not sure if it's me or the authors but I do 
> not believe my question was answered.
> 
> If I have table that has a PK and a FK - will the planner use the FK just same 
> as it would use the PK?  IOW's is a FK also an index used by the planner?  
> 
> I have a lagacy table that contains a FK constraint (vendor_id --> 
> vendor_info).  I believe I need an index to improve the performance of a query 
> because I'm using the column as part of my join.  Explain does not appear to 
> use it as an index (instead of a seq scan it uses a hash join).  But the table 
> all ready has a FK key contraint on the column.

Yes, for large tables you have to create a own index on your fk-column.


Andreas
-- 
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect.                              (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly."   (unknown)
Kaufbach, Saxony, Germany, Europe.              N 51.05082°, E 13.56889°

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