DISTINCT ON not working...?

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От Phillip Smith
Тема DISTINCT ON not working...?
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Msg-id 003f01c75474$d1ce3480$9b0014ac@wbaus090
обсуждение исходный текст
Ответы Re: DISTINCT ON not working...?  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-sql
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) = 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) =
falseTHEN 
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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