Date: Thu, 23 May 2013 11:36:30 -0700 (PDT)
From: David Johnston <polobo@yahoo.com>
To: pgsql-sql@postgresql.org
Message-ID: <1369334190307-5756661.post@n5.nabble.com>
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 <CAAY=A79+vsQN3zzPC7CtSoJFPxbp-Kf=yxg-hdCd6AEb3i6P5Q@mail.gmail.com>
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Subject: Re: Select statement with except clause
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JORGE MALDONADO wrote
> How does the EXCEPT work? Do fields should be identical?
> I need the difference to be on the first 3 fields.

Except operates over the entire tuple so yes all fields are evaluated and,
if they all match, the row from the "left/upper" query is excluded.

If you need something different you can use some variation of:
IN
EXISTS
NOT IN
NOT EXISTS

with a sub-query (correlated or uncorrelated as your need dictates).

For example:

SELECT col1, col2, col3, sum(col4)
FROM tbl
WHERE (col1, col2, col3) NOT IN (SELECT col1, col2, col3 FROM tbl2) -- not
correlated
GROUP BY col1, col2, col3

SELECT col1, col2, col3, sum(col4)
FROM tbl
WHERE NOT EXISTS (
  SELECT 1 FROM tbl AS tbl2 WHERE --make sure to alias the sub-query table
if it matches the outer reference
  (tbl.col1, tbl.col2, tbl.col3) = (tbl2.col1, tbl2.col2, tbl2.col3)
) -- correlated; reference "tbl" within the query inside the where clause
GROUP BY col1, col2, col3

I do not follow your example enough to provide a more explicit
example/solution but this should at least help point you in the right
direction.

David J.


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