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From: David G Johnston <david.g.johnston@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Re: Problem with duplicate rows when FULL OUTER JOIN'ing 3 derived tables
Date: Thu, 12 Jun 2014 07:02:39 -0700 (PDT)
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Note - numbers do not relate to your questions. This pretty much answers 1
and 3.

1. I'd ensure that project name/id on a table can never be null by creating
a dummy project that means "none assigned".
2. I would avoid full join.  To do so I'd cross join a distinct list of
companies with a distinct list of projects.
3. Against the join in 2 you then left join three times, once for each
product table.
4. In the final result any product not having a correspond company/project
would have its value coalesced to zero.

The end result is a table without any NULL and, in the case of your
explanatory data, 9 rows - two of which would be all zeros: (c3,p1) and
(c3,p,2)

If you cannot change the raw data I'd use CTE/WITH to normalize the data
according to 1 and the use these CTEs in the rest of the query.  I would
also do 2 is a CTE then 3 would be normal subqueries or relation references
as necessary.

David J.



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