Re: Fix numeric log() with an infinite value and 0<base<=1

On Thu, 15 Oct 2026 at 04:16, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:
>
>
>
> > On Oct 14, 2026, at 23:07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com> writes:
> >
> >> So, I'd suggest something like
> >
> >> + if (cmp_var(, const_one) == 0)
> >> + ereport(ERROR,
> >> + errcode(ERRCODE_INVALID_ARGUMENT_FOR_LOG),
> >> + errmsg("cannot take logarithm using base 1"));
> >
> > Agreed, but if we want that, we must do it for a finite second input
> > too. Right now you do get
> >
> > regression=# select log(1, 33);
> > ERROR: division by zero
> >
> > Chao proposes matching that, which isn't insane, but I like a
> > specialized error message better.
> >
>
> That’s why I chose that error message, because the existing test has this:
> ```
> select log(1.0, 12.34);
> ERROR: division by zero
> ```

Ah, I see, thanks for clarifying. This wasn't quite clear from the
initial post.

> After thinking it over, I think we can add a check for base 1 in log_var(), and numeric_log() can just defer base 1 handling to log_var(). Please see v2, which implements this approach.

LGTM.

Kind regards,

Matthias van de Meent
Databricks (https://www.databricks.com)