Re: distinct on
- From: Thomas Kellerer <thomas.kellerer@xxxxxxxxxx>
- To: "oracle-l@xxxxxxxxxxxxx >> \"oracle-l@xxxxxxxxxxxxx\"" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 18 Oct 2012 09:05:29 +0200
Jonathan Lewis, 18.10.2012 08:57:
>
> How does the Postgres specification define the requirements for the columns
> other than the on() column ?
>
> Is it "one row at (pseudo-)random from all the rows which match this
> specific value of the on() column", or is there any indication that the
> other columns could ALL be chosen randomly so that the output wasn't a row
> that actually existed, or is there any indication that the result will be
> deterministic in a particular way ?
>
It uses the ordering defined by the ORDER BY if there is one, otherwise it's
undefined:
From the manual:
"Note that the "first row" of each set is unpredictable unless ORDER BY is
used to ensure that the desired row appears first"
So in the originally posted example it *is* actually undefined as no ORDER BY
was used
The "equivalent" (of undefined) in my solution using row_number() would be to
remove the order by in the over() clause
Thomas
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