function pl sql with select
CREATE OR REPLACE FUNCTION get_total_sales(
in_year PLS_INTEGER
)
RETURN NUMBER
IS
l_total_sales NUMBER := 0;
BEGIN
-- get total sales
SELECT SUM(unit_price * quantity)
INTO l_total_sales
FROM order_items
INNER JOIN orders USING (order_id)
WHERE status = 'Shipped'
GROUP BY EXTRACT(YEAR FROM order_date)
HAVING EXTRACT(YEAR FROM order_date) = in_year;
-- return the total sales
RETURN l_total_sales;
END;