Re: count(*) vs count(id)

Le mar. 2 févr. 2021 à 02:14, Matt Zagrabelny <mzagrabe(at)d(dot)umn(dot)edu> a écrit :

>
>
> On Mon, Feb 1, 2021 at 6:35 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Matt Zagrabelny <mzagrabe(at)d(dot)umn(dot)edu> writes:
>> > On Mon, Feb 1, 2021 at 5:57 PM Rob Sargent <robjsargent(at)gmail(dot)com>
>> wrote:
>> >> You got one null from count(*) likely.
>>
>> > What is count(*) counting then? I thought it was rows.
>>
>> Yeah, but count(id) only counts rows where id isn't null.
>>
>
> I guess I'm still not understanding it...
>
> I don't have any rows where id is null:
>
> $ select count(*) from call_records where id is null;
> count
> ═══════
> 0
> (1 row)
>
> Time: 0.834 ms
> $
>
> select count(id) from call_records where id is null;
> count
> ═══════
> 0
> (1 row)
>
> Time: 0.673 ms
>
> Which field is count(*) counting if it is counting nulls?
>

You're doing a left join, so I guess there's no row where
call_records.timestamp::date = 2020-08-30. That would result with a NULL id.

Guillaume