Re: Allow to collect statistics on virtual generated columns

On Wed, 25 Mar 2026 13:01:27 +0900
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> wrote:

> On Tue, 24 Mar 2026 11:43:47 +0000
> Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>
> > On Tue, 24 Mar 2026 at 10:57, Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> wrote:
> > >
> > > One concern is that CREATE STATISTICS does not allow creating extended
> > > statistics on a single colmun. If we try this, it raises the following error:
> > >
> > > ERROR: extended statistics require at least 2 columns
> > >
> > > Therefore, if we take this approach, we would need to add an exception
> > > to this rule for virtual columns.
> >
> > I think that would be fine. It makes sense because a virtual column
> > expands to an expression, and we already allow CREATE STATISTICS on a
> > single expression.
>
> I've attached a patch updated along these lines.
>
> This allows users to define extended statistics on virtual generated
> columns. Expressions including such columns are stored in the catalog
> as-is, and expanded at ANALYZE time. Extended statistics on a single
> virtual generated column are also allowed, since it is treated as a
> single expression.
>
> To enable the optimizer to make use of these statistics, expressions
> are also expanded at planning time.
>
> Additional documentation and tests are needed, but are not yet included.
>
> Is this approach better then the previous one?

I've attached an updated patch including the documentation and tests.

Regards,
Yugo Nagata

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>