From: Tom Lane <tgl@sss.pgh.pa.us>
To: jwwfou@gmail.com
cc: pgsql-docs@lists.postgresql.org
Subject: Re: Possibly Incorrect Data Return
In-reply-to: <166794307526.652.9073408178177444190@wrigleys.postgresql.org>
References: <166794307526.652.9073408178177444190@wrigleys.postgresql.org>
Comments: In-reply-to PG Doc comments form <noreply@postgresql.org>
	message dated "Tue, 08 Nov 2022 21:31:15 +0000"
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Date: Tue, 08 Nov 2022 17:22:24 -0500
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PG Doc comments form <noreply@postgresql.org> writes:
> Hello: I am working through the tutorial and the Doc page says the row count
> is 5 but my results show 0 records. Of course, I may be doing something
> wrong, too:

> jwjwj=# SELECT city, max(temp_lo), count(*) FILTER (WHERE temp_lo < 30)
>     FROM weather
>     GROUP BY city
>     HAVING max(temp_lo) < 40;
>   city   | max | count 
> ---------+-----+-------
>  Hayward |  37 |     0
> (1 row)

No, you're right, given the sample data shown earlier then count = 0
is what you would get.  Somebody injected this FILTER example without
a lot of thought, it would appear, as not only does the output not
match but it's completely disjointed from the flow of explanation
(IMO anyway).  This example originally introduced only HAVING, and
trying to make it do double duty just confuses things.  A fully
separate example of FILTER would have served better.

I'll go do something about that --- thanks for the report!

			regards, tom lane