[英]Can I combine these two SQL queries into one?
drink_orders
有很多drink_order_extras
首先:
SELECT
Sum(drink_orders.quantity * drink_orders.drink_price) AS drink_total
FROM
drink_orders
WHERE
drink_orders.reservation_id = 3610
第二个
SELECT
Sum(drink_order_extras.quantity * drink_order_extras.drink_price) AS extra_total
FROM
drink_order_extras INNER JOIN
drink_orders ON drink_order_extras.drink_order_id = drink_orders.id
WHERE
drink_orders.reservation_id = 3610
获得总计也很不错(drink_total + extra_total)
仅供参考,下面不会导致正确的总和:
SELECT
Sum(drink_orders.quantity * drink_orders.drink_price) AS drink_total,
Sum(drink_order_extras.quantity * drink_order_extras.drink_price) AS extra_total
FROM
drink_order_extras INNER JOIN
drink_orders ON drink_order_extras.drink_order_id = drink_orders.id
WHERE
drink_orders.reservation_id = 3610
编辑:
Gordon Linoff的回答非常好:
SELECT Sum(do.quantity * do.drink_price) AS drink_total,
Sum(extras_total) as extras_total,
(Sum(do.quantity * do.drink_price) + COALESCE(Sum(extras_total), 0)
) as total
FROM drink_orders do LEFT JOIN
(SELECT doe.drink_order_id,
Sum(doe.quantity * doe.drink_price) as extras_total
FROM drink_order_extras doe
GROUP BY drink_order_id
) doe
ON do.id = doe.drink_order_id
WHERE do.reservation_id = 3610;
你在两个不同的维度上进行求和。 join
导致笛卡尔积 - 抛出总和。 您可以在加入之前通过聚合来解决此问题:
SELECT Sum(do.quantity * do.drink_price) AS drink_total,
Sum(extras_total) as extras_total,
(Sum(do.quantity * do.drink_price) + COALESCE(Sum(extras_total), 0)
) as total
FROM drink_orders do LEFT JOIN
(SELECT doe.drink_order_id,
Sum(doe.quantity * doe.drink_price) as extras_total
FROM drink_orders_extras doe
GROUP BY drink_order_id
) doe
ON do.id = doe.drink_order_id
WHERE do.reservation_id = 3610;
这首先将额外费用计入饮品订单。 然后它将所有饮料订单信息汇总为预订级别。
尝试这个:
select sum(total) from (
SELECT
Sum(drink_orders.quantity * drink_orders.drink_price) AS total
FROM
drink_orders
WHERE
drink_orders.reservation_id = 3610
UNION
SELECT
Sum(drink_order_extras.quantity * drink_order_extras.drink_price) AS total
FROM
drink_order_extras INNER JOIN
drink_orders ON drink_order_extras.drink_order_id = drink_orders.id
WHERE
drink_orders.reservation_id = 3610
) t
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