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From: Mark Williams <markwillimas@gmail.com>
To: 'David G. Johnston' <david.g.johnston@gmail.com>
Cc: 'pgsql-sql' <pgsql-sql@lists.postgresql.org>
Subject: RE: Select Distinct Order By Array_Position
Date: Mon, 26 Nov 2018 19:59:55 -0000
Message-ID: <005301d485c2$9a6f1db0$cf4d5910$@gmail.com> (raw)
In-Reply-To: <CAKFQuwYroR1Q_+rF6odeDEA5+NLk6TjCYy-yTJUxf+ob7huhdg@mail.gmail.com>
References: <004301d485bc$00347250$009d56f0$@gmail.com>
	<CAKFQuwYroR1Q_+rF6odeDEA5+NLk6TjCYy-yTJUxf+ob7huhdg@mail.gmail.com>

David, thanks. It was a bad example on my part. Could just as well have been: (26194, 189, 2345).

__

-----Original Message-----
From: David G. Johnston <david.g.johnston@gmail.com> 
Sent: 26 November 2018 19:46
To: Mark Williams <markwillimas@gmail.com>
Cc: pgsql-sql <pgsql-sql@lists.postgresql.org>
Subject: Re: Select Distinct Order By Array_Position

On Mon, Nov 26, 2018 at 12:12 PM Mark Williams <markwillimas@gmail.com> wrote:
> I am ordering by documents.id and it appears in my select list.
[...]
> SELECT DISTINCT documents.id, page_no FROM texts LEFT JOIN documents 
> on documents.id=texts.doc_id WHERE doc_id IN (26194, 2345, 189) AND  
> (text LIKE '%RIVER%') ORDER BY array_position(ARRAY[26194, 2345, 
> 189]::INTEGER[], documents.id)

No, you are not ordering by documents.id, you are ordering by an expression into which you are passing the documents.id value as one of its components.

When you use ORDER BY and DISTINCT together you basically are short-handing:

SELECT sq.*
FROM (SELECT DISTINCT ...) AS sq
ORDER BY sq.?

If you want to order by something you have to include it exactly in the select-list of the inner/distinct query.

In this example, though, you could just "ORDER BY documents.id DESC"...

David J.

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