Oracle: MAX of SUM of each Group

Question

我的方案是使用子查询显示每个酒店分店维护成本最高的酒店房间。我有三个单独的表：branch、room 和 maintenance。

表branch

id             NUMBER(3) PRIMARY KEY
location       VARCHAR2(20)

表room

id             NUMBER(3) PRIMARY KEY
room_number    CHAR(4)
branch_id      NUMBER(3)

表maintenance

id             NUMBER(3) PRIMARY KEY
room_id        NUMBER(3)
cost           NUMBER(4)

我想要的输出格式为

location | room_number | cost
-------------------------------
         |             |
         |             |
         |             |

在添加每个房间的总成本后，我不确定如何选择每个分支的最大值。请指教。

Answer 1

你可以使用窗口函数：

select *
from (
    select b.location, r.room_number, m.cost, 
        rank() over(partition by b.id order by m.cost desc) rn
    from branch b
    inner join room r on r.branch_id = b.id
    inner join maintenance m on m.room_id = r.id
) t
where rn = 1

如果一个房间可能有多次维护，那么我们需要聚合：

select *
from (
    select b.location, r.room_number, sum(m.cost) as cost, 
        rank() over(partition by b.id order by sum(m.cost) desc) rn
    from branch b
    inner join room r on r.branch_id = b.id
    inner join maintenance m on m.room_id = r.id
    group by b.id, b.location, r.room_number
) t
where rn = 1

Answer 2

您可以使用ROW_NUMBER() 分析函数来加入这些表

SELECT location, room_number, cost
  FROM (SELECT b.location,
               r.room_number,
               m.cost,
               ROW_NUMBER() OVER(PARTITION BY r.branch_id ORDER BY m.cost DESC) AS rn
          FROM branch b
          JOIN room r
            ON r.branch_id = b.id
          JOIN maintenance m
            ON m.room_id = r.id)
 WHERE rn = 1

附注如果关系（成本的相等值）很重要（即使生成额外的最大成本值行没有问题，也应该包括在内），那么您可以将 ROW_NUMBER() 替换为 DENSE_RANK()