| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Marcos Pegoraro <marcos(at)f10(dot)com(dot)br> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Eisentraut <peter(at)eisentraut(dot)org>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Document NULL |
| Date: | 2024-12-12 16:35:08 |
| Message-ID: | CAKFQuwYzChK7Y_XnU1QD-rJEOxML93DuR_z6tR69f7f=83i+kw@mail.gmail.com |
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On Wed, Dec 11, 2024 at 11:46 AM Marcos Pegoraro <marcos(at)f10(dot)com(dot)br> wrote:
> Em ter., 10 de dez. de 2024 às 20:00, David G. Johnston <
>> david(dot)g(dot)johnston(at)gmail(dot)com> escreveu:
>>
>
> Section nullvalues-filtering you are showing filtering with equal and not
> equal. Wouldn't it be better if you show just one of them and the other
> using DISTINCT FROM, which would get different results ?
>
>
I'm demonstrating the sentence written there -
A WHERE clause that evaluates to a null value for a given row will exclude
that row.
While I can do that with a single example my intent here was to also
show that if one writes seemingly mutually exclusive expressions in a where
clause it is possible neither expression will find a row, in this case with
id=2. "p OR !p" again. I'll give this some more thought though.
In any case I do need to add a few more words framing up the examples.
Probably pointing back to the cardinal rule sub-section.
David J.
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