indexes bug or feature

--- Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> You don't need to post questions four times ;-)
>
> Heni Lolov <hal_bg(at)yahoo(dot)com> writes:
> > I have folowing table
>
> > create table usno(
> > reg_id int2,
> > id int2,
> > ra int4,
> > de int4,
> > mag_r int2,
> > mag_b int2
> > );
>
> > I make indexes in this order:
> > create index usno_drm_r on gsc_act(de,ra,mag_r);
> > create index usno_drm_b on gsc_act(de,ra,mag_b);
>
> > the problem is:
> > when I search on "de","ra" and "mag_b" or "de",
> "ra"
> > and "mag_r" Postgres uses always "usno_drm_r".
> > If I create the indexes in reversed order
> > "usno_drm_b" is always used.
>
> I bet that it's only using the first two columns of
> the index,
> so that it doesn't really matter which index is
> used. Are you
> being careful to cast the values compared to mag_r
> or mag_b to
> int2? "mag_r = 42" isn't indexable because 42 is an
> int4.

I am sure that the values are int2 and there is no
casting when I am using psql to examine this.

>
> regards, tom lane

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