MySQL左连接，求和和group_by

Question

我有4张桌子。 地区 ， 土地 ， 房屋和货物 。

• 土地有一对一的关系。 与地区 。
• 土地有一对多的关系。 带房子 。
• 房子有一对多的关系。 与货物 。

sqlfiddle ： http : //sqlfiddle.com/#!9/5eaec

当前查询 ：

SELECT
    Sum(land.wide) AS land_wide,
    Sum(house.price) AS house_price,
    Sum(goods.amount) AS goods_amount,
    Sum(goods.price) AS goods_price,
    region.region_name
FROM
    land
LEFT JOIN house ON house.land_id = land.id
LEFT JOIN goods ON goods.house_id = house.id
LEFT JOIN region ON land.region_id = region.id
GROUP BY
    region.region_name
ORDER BY
    region.id ASC

但效果不理想。

期望的输出 ：

+-----------+-------------+-------------+--------------+---------+
| land_wide | house_price | goods_price | goods_amount | region  |
+-----------+-------------+-------------+--------------+---------+
| 510       | 57910       | 1900        | 56           | Tokyo   |
|           |             |             |              | Osaka   |
|           |             |             |              | Nagoya  |
|           |             |             |              | Sapporo |
+-----------+-------------+-------------+--------------+---------+

有人会为我提供一个有帮助的解决方案吗？ 我很确定可以在SQL中完成？

Answer 1

SELECT 
   land_wides.land_wide, 
   house_prices.house_price, 
   goods_amounts_prices.goods_price, 
   goods_amounts_prices.goods_amount, 
   region.region_name
FROM region
LEFT JOIN (SELECT
              Sum(land.wide) AS land_wide,
              region.id AS region_id
           FROM region
           LEFT JOIN land ON land.region_id = region.id
           GROUP BY region.id) land_wides ON region.id = land_wides.region_id
LEFT JOIN (SELECT
              Sum(house.price) AS house_price,
              region.id AS region_id
           FROM region
           LEFT JOIN land ON land.region_id = region.id
           LEFT JOIN house ON house.land_id = land.id
           GROUP BY region.id) house_prices ON region.id = house_prices.region_id
LEFT JOIN (SELECT
              Sum(goods.amount) AS goods_amount,
              Sum(goods.price) AS goods_price,
              region.id AS region_id
           FROM region
           LEFT JOIN land ON land.region_id = region.id
           LEFT JOIN house ON house.land_id = land.id
           LEFT JOIN goods ON goods.house_id = house.id
           GROUP BY region.id) goods_amounts_prices on goods_amounts_prices.region_id = region.id
ORDER BY region.id

Answer 2

左联接应该是内部联接。 您希望对匹配的行进行分组。 没有不匹配的行，因此按总和分组。