conditional FROM

From: Richard Klingler <richard(at)klingler(dot)net>
To: pgsql-sql(at)postgresql(dot)org
Subject: conditional FROM
Date: 2011-12-10 16:03:32
Message-ID: 20111210170332479879.3df30525@klingler.net
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Good day...

I'm trying to build a query for PGSQL 9.1 where a table has two
references with only one being used depending of the type of entry..

For example, the table has following simplified structure:

portid primary key
port2node index to table node
port2card index to table card

So how can I do a conditional FROM clause in the query depending on the
column port2node and port2card?
If port2card is Null or 0 I don't want it in the FROM clause as the
query will return unneccessary duplicate
row...the same goes for port2node being Null or 0...

thanx in advance
richard

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