I really want to do streaming queries over updates and inserts in a normal SQL database. Imagine writing

    SUBSCRIBE SELECT customers.id, customers.name 
    FROM EVENTS(customer_purchases) AS cpe
    LEFT OUTER JOIN customers ON cpe.row.customer_id = customers.id
    WHERE cpe.row.product_id = '123abc' AND cpe.type IN ('update', 'insert') 

in postgres itself and just getting every incoming purchase for a particular product.