Re: doc: Clarify that empty COMMENT string removes the comment

On Thu, Feb 26, 2026 at 2:07 PM Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:

> Hi,
>
> While reviewing patch [1] before the holiday vacation, I noticed that the
> COMMENT ON command treats an empty string as NULL, which effectively
> removes the comment from the object. Today I also saw discussion [2], which
> mentioned the same problem.
>
> From the code, it seems the behavior is intentional:
> ```
> /* Reduce empty-string to NULL case */
> if (comment != NULL && strlen(comment) == 0)
> comment = NULL;
> ```
>
> However, the documentation does not explain this behavior. It currently
> only says:
> ```
> string_literal
> The new comment contents, written as a string literal.
> ```
>
> Is it a common pattern that an empty string is treated as NULL, so that
> the documentation does not need to mention it explicitly? I don’t think so.
> For example, a similar command, SECURITY LABEL ON, treats an empty string
> as just an empty string.
>
> This tiny patch enhances the documentation of COMMENT ON to clarify that
> an empty string is treated as NULL.
>
> [1]
> https://postgr.es/m/e08cb97f-0364-4002-9cda-3c16b42e4136@uni-muenster.de
> [2]
> https://postgr.es/m/CAHGQGwFJKg-aT5vajSU1v_B4K129u_SjZ3EGGHFSBhW967gcMA@mail.gmail.com
>
> Best regards,
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
>
>
>
>
>
Hi Evan,

I've looked at your patch, and I think your change is helpful. I applied it
locally and rendered the html page, it looks good to me.

Thanks!
B.R,
/Shengbin Zhao