Date: Fri, 15 Apr 2005 10:22:27 +0100
From: Stephen Quinney <stephen.quinney@computing-services.oxford.ac.uk>
To: pgsql-sql@postgresql.org
Subject: Combining values in a column
Message-ID: <20050415092227.GA24135@computing-services.oxford.ac.uk>
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I have a query which returns a single column of integers which I want
to combine together with &, "bitwise AND". Basically it's a simple
list of access levels that a user might have and I want to merge the
list into one value. There can be zero, one or more values in the list
so I have to be able to cope with the no-results .

For example

 access
--------
     31
    511

Would lead to 31 & 511 which gives 31.

I guess really this can lead to the more generic question. How do I
apply a general function to combine the values, if I, for example,
wanted to write my own aggregate function like sum?

Thanks in advance,

Stephen Quinney