Re: Question about Foreign key constraint causes "costly

From: Matt Miller <mattm(at)epx(dot)com>
To: emilu(at)cs(dot)concordia(dot)ca
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Question about Foreign key constraint causes "costly
Date: 2005-08-23 14:53:33
Message-ID: 1124808813.4403.15.camel@dbamm01-linux
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On Tue, 2005-08-23 at 10:30 -0400, Emi Lu wrote:
> I'd like to setup foreign key constraint for A.col3, as the following:
> CONSTRAINT Aclo3_fk FOREIGN KEY (col3) REFERENCES B(colB1)
>
> But I got a warning msg from postgresql as:
>
> foreign key constraint "Aclo3_fk" will require costly sequential
> scans

Index the foreign key:

create index a_col3_ix on a (col3);

and then drop an recreate the foreign key and see if the warning is
still there.

As a rule I index foreign keys.

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