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From: "Phillip Smith" <phillip.smith@weatherbeeta.com.au>
To: <pgsql-sql@postgresql.org>
Subject: DISTINCT ON not working...?
Date: Tue, 20 Feb 2007 09:25:11 +1100
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Hi all,

Strange one - I have a nightly export / import routine that exports from =
one
database and imports to another. Has been working fine for several =
months,
but last night it died on a unique constraint.

To cut out all the details, the code that is causing the problem:
        SELECT  DISTINCT ON (ean)
                code,
                CASE WHEN ean IS NULL OR valid_barcode(ean) =3D false =
THEN
null ELSE ean END AS ean
        FROM    TMPTABLE
        WHERE   code NOT IN (SELECT code FROM stock_deleted)
         AND    ean IS NOT NULL

That is the code that generates the error on the unique constraint =
against
the ean column.

If I play with that and run this:
	SELECT  DISTINCT ON (ean)
                CASE WHEN ean IS NULL OR valid_barcode(ean) =3D false =
THEN
null ELSE ean END AS ean,
		    count(*)
        FROM    TMPTABLE
        WHERE   code NOT IN (SELECT code FROM stock_deleted)
         AND    ean IS NOT NULL
	  GROUP BY ean

I get a several thousand rows returned, all with a count(*) of 1, except =
one
row:
	3246576919422	2

DISTINCT ON should eliminate one of those rows that is making that 2 - =
as I
said, it's been working fine for several months, and it is still doing =
it
correctly for approximately 100 other rows that have duplicate ean =
codes.

Can anyone give me a hand to work out why this one is doubling up?!

Cheers,
~p


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