Re: Composite keys

On Tue, Oct 11, 2011 at 8:52 PM, Claudio Freire <klaussfreire@gmail.com> wrote:
> On Tue, Oct 11, 2011 at 5:16 PM, Carlo Stonebanks
> <stonec.register@sympatico.ca> wrote:
>> Question 2) Regardless of the answer to Question 1 - if another_id is not
>> guaranteed to be unique, whereas pkey_id is – there any value to changing
>> the order of declaration (more generally, is there a performance impact for
>> column ordering in btree composite keys?)
>
> Multicolumn indices on (c1, c2, ..., cn) can only be used on where
> clauses involving c1..ck with k<n.

I don't think that's true.  I believe it can be used for a query that
only touches, say, c2.  It's just extremely inefficient.

--
Robert Haas
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