CREATE OR REPLACE FUNCTION public.rewards_report(min_monthly_purchases integer, min_dollar_amount_purchased numeric)
 RETURNS SETOF customer
 LANGUAGE plpgsql
 SECURITY DEFINER
AS $function$
DECLARE
    last_month_start DATE;
    last_month_end DATE;
rr RECORD;
tmpSQL TEXT;
BEGIN

    /* Some sanity checks... */
    IF min_monthly_purchases = 0 THEN
        RAISE EXCEPTION 'Minimum monthly purchases parameter must be > 0';
    END IF;
    IF min_dollar_amount_purchased = 0.00 THEN
        RAISE EXCEPTION 'Minimum monthly dollar amount purchased parameter must be > $0.00';
    END IF;

    last_month_start := CURRENT_DATE - '3 month'::interval;
    last_month_start := to_date((extract(YEAR FROM last_month_start) || '-' || extract(MONTH FROM last_month_start) || '-01'),'YYYY-MM-DD');
    last_month_end := LAST_DAY(last_month_start);

    /*
    Create a temporary storage area for Customer IDs.
    */
    CREATE TEMPORARY TABLE tmpCustomer (customer_id INTEGER NOT NULL PRIMARY KEY);

    /*
    Find all customers meeting the monthly purchase requirements
    */

    tmpSQL := 'INSERT INTO tmpCustomer (customer_id)
        SELECT p.customer_id
        FROM payment AS p
        WHERE DATE(p.payment_date) BETWEEN '||quote_literal(last_month_start) ||' AND '|| quote_literal(last_month_end) || '
        GROUP BY customer_id
        HAVING SUM(p.amount) > '|| min_dollar_amount_purchased || '
        AND COUNT(customer_id) > ' ||min_monthly_purchases ;

    EXECUTE tmpSQL;

    /*
    Output ALL customer information of matching rewardees.
    Customize output as needed.
    */
    FOR rr IN EXECUTE 'SELECT c.* FROM tmpCustomer AS t INNER JOIN customer AS c ON t.customer_id = c.customer_id' LOOP
        RETURN NEXT rr;
    END LOOP;

    /* Clean up */
    tmpSQL := 'DROP TABLE tmpCustomer';
    EXECUTE tmpSQL;

RETURN;
END
$function$