如何从非规范化 table 计算未膨胀的 SUM

Question

这是建立在之上的。假设我有一个非规范化的 table 看起来像这样：

    Apple_ID | Tree_ID | Orchard_ID | Tree_Height | ...other columns...
   ---------------------------------------------------------------------
           1 |       1 |          1 |          12 |  ...other values...
   ---------------------------------------------------------------------
           2 |       1 |          1 |          12 |  ...other values...
   ---------------------------------------------------------------------
           3 |       1 |          1 |          12 |  ...other values...
   ---------------------------------------------------------------------
           4 |       2 |          1 |          15 |  ...other values...
   ---------------------------------------------------------------------
           5 |       2 |          1 |          15 |  ...other values...
   ---------------------------------------------------------------------
           6 |       2 |          1 |          15 |  ...other values...
   ---------------------------------------------------------------------
           7 |       2 |          1 |          15 |  ...other values...
   ---------------------------------------------------------------------
           8 |       3 |          1 |          20 |  ...other values...
   ---------------------------------------------------------------------
           9 |       3 |          1 |          20 |  ...other values...
   ---------------------------------------------------------------------
          10 |       4 |          2 |          30 |  ...other values...
   ---------------------------------------------------------------------
          11 |       5 |          2 |          10 |  ...other values...
   ---------------------------------------------------------------------
          12 |       5 |          2 |          10 |  ...other values...
   ---------------------------------------------------------------------
          13 |       5 |          2 |          10 |  ...other values...
   ---------------------------------------------------------------------

我想计算每个果园Tree_Heights的总和，所以我要取回的结果是：

Orchard_ID | sum(Tree_Height)
-------------------------------
         1 |               47
-------------------------------
         2 |               40

但是，由于非规范化，总和膨胀为：

Orchard_ID | sum(Tree_Height)
-------------------------------
         1 |              136
-------------------------------
         2 |               60

我之前提到的问题的解决方案在这里无法实现，因为我们不能通过唯一的行列来求和（）。我怎样才能编写一个简单的查询来获得预期的结果？

Answer 1

最简单的写法是使用 CTE，但如果您的系统不支持，您可以使用派生的 table。我们对每棵树在 Apple_ID 上使用 ROW_NUMBER() 来给我们一个独特的行来求和：

SELECT "Orchard_ID", SUM("Tree_Height") AS Total_Height
FROM (
  SELECT "Orchard_ID", "Tree_Height", 
         ROW_NUMBER() OVER (PARTITION BY "Orchard_ID", "Tree_ID" ORDER BY "Apple_ID") AS rn
  FROM data
) d
WHERE rn = 1
GROUP BY "Orchard_ID"

输出

Orchard_ID  total_height
1           47
2           40

如果你可以使用 CTEs，它会这样写：

WITH CTE AS (
  SELECT "Orchard_ID", "Tree_Height", 
         ROW_NUMBER() OVER (PARTITION BY "Orchard_ID", "Tree_ID" ORDER BY "Apple_ID") AS rn
  FROM data
)
SELECT "Orchard_ID", SUM("Tree_Height") AS Total_Height
FROM CTE
WHERE rn = 1
GROUP BY "Orchard_ID"

Demo on SQLFiddle

如何从非规范化 table 计算未膨胀的 SUM

How to calculate a non-inflated SUM from a denormalized table

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