function pl sql with select

CREATE FUNCTION function_name … RETURN BOOLEAN IS
	Definitions;
BEGIN
	Statement;
	RETURN "Hello World!";
END;

 
     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;