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Thread: foreign key is it a real key

foreign key is it a real key

From
John Fabiani
Date:
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

Re: foreign key is it a real key

From
Andreas Kretschmer
Date:
John Fabiani <johnf@jfcomputer.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°

Re: foreign key is it a real key

From
John Fabiani
Date:
On Monday, February 13, 2012 04:50:47 PM Andreas Kretschmer wrote:
> John Fabiani <johnf@jfcomputer.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

Thanks
Johnf