온라인 쇼핑몰의 월 별 매출액 집계 : solvesql

SELECT  DATE_FORMAT(o.order_date, '%Y-%m') as order_month,
        SUM(CASE WHEN LEFT(oi.order_id, 1) <> 'C' THEN oi.price * oi.quantity ELSE 0 END) as ordered_amount,
        SUM(CASE WHEN LEFT(oi.order_id, 1) = 'C' THEN oi.price * oi.quantity ELSE 0 END) as canceled_amount,
        SUM(oi.price * oi.quantity) as total_amount
FROM    orders o INNER JOIN order_items oi
        ON o.order_id = oi.order_id
GROUP BY
        DATE_FORMAT(o.order_date, '%Y-%m')
ORDER BY
        order_month