Why does a simple query not use an obvious index?

The query:
select count(*) from billing where timestamp > now()-60

should obviously use the index

CREATE INDEX billing_timestamp_idx ON billing USING btree ("timestamp"
timestamp_ops);

on a table with 1400000 rows.

But it uses a Seq Scan. If I set enable_seqscan=no, it indicates a queryplan
could not be calculated.

Why does this simple query not use the timestamp index, and how can I get it
to?

Thanks, Jack

Jack Kerkhof
Research & Development
jack(dot)kerkhof(at)guest-tek(dot)com
www.guest-tek.com
1.866.509.1010 3480

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