Re: Boolean column in multicolumn index

Will that bug be fixed?

The problem is that if I use partial indexes I will have to create 3 of
them:

CREATE INDEX partial_1 ON public.t USING btree (ci, co) WHERE cb IS TRUE;
CREATE INDEX partial_2 ON public.t USING btree (ci, co) WHERE cb IS FALSE;
CREATE INDEX partial_3 ON public.t USING btree (ci, co) WHERE cb IS NULL;

And if I have 2 booleans columns in index, then it will be 9 combinations.

On Sun, Dec 11, 2016 at 5:04 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Dima Pavlov <imyfess(at)gmail(dot)com> writes:
> > Test table and indexes:
> > ------------------------
>
> > CREATE TABLE public.t (id serial, cb boolean, ci integer, co integer)
>
> > INSERT INTO t(cb, ci, co)
> > SELECT ((round(random()*1))::int)::boolean, round(random()*100),
> > round(random()*100)
> > FROM generate_series(1, 1000000)
>
> > CREATE INDEX "right" ON public.t USING btree (ci, cb, co);
> > CREATE INDEX wrong ON public.t USING btree (ci, co);
> > CREATE INDEX right_hack ON public.t USING btree (ci, (cb::integer), co);
>
> > The problem is that I can't force PostgreSQL to use the "right" index.
>
> Hmm. Poking at this, it seems not to realize that the cb column is
> rendered irrelevant to the index ordering, ie it doesn't notice that
> using "right" would allow skipping the sort step. That's a bug,
> likely due to the hacking that goes on to allow "cb" and "cb = true"
> to both be considered indexable conditions.
>
> But probably the reason nobody's noticed before is that it's quite
> uncommon to have boolean columns in indexes. If you're only concerned
> about doing this with "cb = TRUE", you might consider
>
> CREATE INDEX partial ON public.t USING btree (ci, co) WHERE cb;
>
> regards, tom lane
>