Re: [PATCH] Replace COUNT(NULL) with '0'::bigint

On Sun, 25 Jan 2026 at 19:48, Junwang Zhao <zhjwpku(at)gmail(dot)com> wrote:
> In [1], David Rowley noted that COUNT(NULL) can be replaced
> with '0'::bigint. The change should be straightforward, and I came
> up with the attached patch to implement it.
>
> [1] https://www.postgresql.org/message-id/CAApHDvrde9DUpQ3DhPd3ia9tchVmhZqewfzxSYWmYFWVj%3DLPpg%40mail.gmail.com

Coming up with the code to do this wasn't the problem. I already
posted it in the patch in [2]. The reason I didn't commit that part is
simply that I don't think anyone would ever write COUNT(NULL) in a
query. My opinion has not changed since I wrote [3]. The main reason I
even mentioned COUNT(NULL) is because I wanted the API to support
replacing the Aggref with some other Node type, and that was the only
example I could think of to test to ensure it worked. I had hoped that
someone might come up with some ideas to do that which might be more
applicable in the real world, rather than regurgitate ideas I'd
thought of but didn't think were useful.

Do you really feel like this is useful to anyone? or did you just
write the patch because you can?

Corey did mention in [4] that he is in favour, so maybe it's just me
who thinks it's useless... Perhaps someone else wants to commit it.

David

[2] https://postgr.es/m/CAApHDvppFVDdjpYrs%3DpwgCnp-jv-tneQyfu8rWM8ymHcuJOJYw%40mail.gmail.com
[3] https://postgr.es/m/CAApHDvppFVDdjpYrs%3DpwgCnp-jv-tneQyfu8rWM8ymHcuJOJYw%40mail.gmail.com
[4] https://postgr.es/m/CADkLM%3De2Rb%2Bs3TV3LgYx8O1z2Cs%2BX2FSoafd6%3DUzpPD7hiocfw%40mail.gmail.com