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Subject: 
From: "TJ O'Donnell" <tjo@acm.org>
To: <stephen.quinney@computing-services.oxford.ac.uk>
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There some documentation about aggregate functions in the manual, for example:
http://www.postgresql.org/docs/7.4/static/sql-createaggregate.html

Here's a simple agg function that should work for you,
assuming your col types are int4.

CREATE AGGREGATE andsum (
 sfunc = int4and,
 basetype = int4,
 stype = int4
);

TJ