Igor,
Here's the example where a partial index can "hide" rows.
>From the wikipedia article cited by the OP:
<wikipedia>
It is not necessary that the condition be the same as the index criterion;
Stonebraker's paper below presents a number of examples with indexes similar
to the following:
create index partial_salary on employee(age) where salary > 2100;
</wikipedia>
What would happen if you issued these queries?
select max(age) from employee
select avg(age) from employee
Would the ages of employees earning <= 2100 be included? Is the
partial-index used under those circumstances?
--
Tim Romano
On Thu, Aug 19, 2010 at 9:16 PM, Igor Tandetnik <itandet...@mvps.org> wrote:
> Tim Romano <tim.romano...@gmail.com> wrote:
> > How would you find a row whose column X contained value Y if the
> "partial"
> > index on column X specified that rows containing value Y in column X
> should
> > never be returned?
>
> No one suggests partial index should be capable of hiding anything. The
> idea is that, when the query can be proven to only involve rows covered by
> the partial index, the index can be used to speed up the query. Otherwise,
> it simply won't be used.
> --
> Igor Tandetnik
>
>
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