From: Rob Sargent <robjsargent@gmail.com>
To: Richard Broersma <richard.broersma@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Re: left outer join on more than 2 tables?
Date: Tue, 16 Jun 2009 17:12:59 -0600
Message-ID: <4A3826FB.8090907@gmail.com> (raw)
In-Reply-To: <396486430906161550v30befebelcfddd58ebc4b4f2d@mail.gmail.com>
References: <4A3807CF.90109@consumercontact.com>
<396486430906161425i1cb7949enff5443cc2043805a@mail.gmail.com>
<4A38114B.7090106@gmail.com>
<396486430906161550v30befebelcfddd58ebc4b4f2d@mail.gmail.com>
Richard Broersma wrote:
> On Tue, Jun 16, 2009 at 2:40 PM, Rob Sargent<robjsargent@gmail.com> wrote:
>
>
>> Is there a city without a reference to region?
>>
>
> I don't know, but the OP wanted to know complaints by region.
>
>
I didn't try this, but with regionless cities, you may need a full join
if you want a complete accounting of all complaints, some being logged
to the null region.
>
>
>
>> And wouldn't you want to count(cm.id)?
>>
>
> Count(cm.id) and Count(*) produce the same result. But I like
> Count(*) more since it helps to correctly express the idea that we are
> counting rows per group and not cm.id(s) per group.
>
>
>
>
"Same result" is not true. I loaded tables.
Using count(*) you get count=1 for regions without complaints. Using
count(complaint.id) you get count = 0. (The deference amount to
counting the left hand side (region) vs the right hand side (complaint)
which I believe is what OP is after).
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To: pgsql-sql@postgresql.org
Cc: robjsargent@gmail.com, richard.broersma@gmail.com
Subject: Re: left outer join on more than 2 tables?
In-Reply-To: <4A3826FB.8090907@gmail.com>
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