กำไรรายเดือน

-- Set up the revenue CTE
WITH revenue AS ( 
	SELECT
		DATE_TRUNC('month', order_date) :: DATE AS delivr_month,
		___ AS revenue
	FROM meals
	JOIN orders ON meals.meal_id = orders.meal_id
	GROUP BY delivr_month),
-- Set up the cost CTE
  cost AS (
 	SELECT
		DATE_TRUNC('month', stocking_date) :: DATE AS delivr_month,
		___ AS cost
	FROM meals
    JOIN stock ON meals.meal_id = stock.meal_id
	GROUP BY delivr_month)
-- Calculate profit by joining the CTEs
SELECT
	___,
	___
FROM revenue
JOIN cost ON revenue.delivr_month = cost.delivr_month
ORDER BY revenue.delivr_month ASC;