From: | David Johnston <polobo(at)yahoo(dot)com> |
---|---|
To: | Richard Klingler <richard(at)klingler(dot)net> |
Cc: | "pgsql-sql(at)postgresql(dot)org" <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: conditional FROM |
Date: | 2011-12-10 16:28:29 |
Message-ID: | 2BBB44CA-7EFA-4084-906F-6CB72AD28C6E@yahoo.com |
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Thread: | |
Lists: | pgsql-sql |
On Dec 10, 2011, at 11:03, Richard Klingler <richard(at)klingler(dot)net> wrote:
> 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
>
>
Two options (one of which may not work for you).
1. Write two queries, one for each table, and union the results.
2. Use LEFT JOINs (somehow...)
David J.
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