Re: how to effectively SELECT new "customers"

Without incorporating additional meta-data about the purchases onto the
customer table the most basic solution would be:

SELECT DISTINCT customer_id FROM products WHERE date > (now() - '12
months'::interval)
EXCEPT
SELECT DISTINCT customer_id FROM products WHERE date <= (now() - '12
months'::interval)

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Another solution:
WHERE ... >12 AND NOT EXISTS (SELECT ... WHERE <= 12)

David J.