Обсуждение: Multiple column index question.

If I have an index that's composed of 2 columns:
    Index index1 on tableA (foo,bar)

and I then:
    Select cola, colb from tableA where foo=<value>

Will index1 still be used, or am I looking at a seqscan under all
circumstances in this case?

TIA
-jan m

On Fri, Jan 19, 2007 at 15:22:12 -0500,
  Jan Muszynski <jan@jancm.org> wrote:
> If I have an index that's composed of 2 columns:
>     Index index1 on tableA (foo,bar)
>
> and I then:
>     Select cola, colb from tableA where foo=<value>
>
> Will index1 still be used, or am I looking at a seqscan under all
> circumstances in this case?

The planner can decide to use it. It may not always use it though depending
on what it thinks the costs of the various ways to do the query are.