From: John Fabiani <johnf@jfcomputer.com>
To: pgsql-sql@postgresql.org
Subject: foreign key is it a real key
Date: Mon, 13 Feb 2012 07:46:31 -0800
Message-ID: <5075215.HTHcEtzjPG@linux-12>
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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.

Thanks in advance,

Johnf