具有多个父项的父子层次结构扁平化

Question

我的源结构中有一个父子层次结构，其中子级可以指向他的父级，而他的父级可以存在多行。如果我们扁平化层次结构，这意味着每个子行都需要存在于其父行之下。

下图说明

我已经想好了如何在 T-SQL 中以高效的方式解决这个问题，因为我的源集有 30 万行，这将导致繁重的处理。非常感谢帮助！

直接从上面的示例开始的代码见下文。

SELECT *
INTO Orders
FROM (SELECT CAST('A' AS NVARCHAR(1)) AS Id, CAST('' AS NVARCHAR(1)) AS ParentId, CAST(10 AS int) AS Qty UNION ALL
SELECT CAST('A' AS NVARCHAR(1)) AS Id, CAST('' AS NVARCHAR(1)) AS ParentId, CAST(20 AS int) AS Qty UNION ALL
SELECT CAST('B' AS NVARCHAR(1)) AS Id, CAST('A' AS NVARCHAR(1)) AS ParentId, CAST(30 AS int) AS Qty UNION ALL
SELECT CAST('B' AS NVARCHAR(1)) AS Id, CAST('A' AS NVARCHAR(1)) AS ParentId, CAST(40 AS int) AS Qty UNION ALL
SELECT CAST('C' AS NVARCHAR(1)) AS Id, CAST('B' AS NVARCHAR(1)) AS ParentId, CAST(50 AS int) AS Qty UNION ALL
SELECT CAST('C' AS NVARCHAR(1)) AS Id, CAST('B' AS NVARCHAR(1)) AS ParentId, CAST(60 AS int) AS Qty UNION ALL
SELECT CAST('C' AS NVARCHAR(1)) AS Id, CAST('B' AS NVARCHAR(1)) AS ParentId, CAST(70 AS int) AS Qty) AS T1

Answer 1

我不知道为什么你会想要这样做，但我会这样做...

SELECT
  L1.ID,
  L2.ID,
  L3.ID,
  COALESCE(L3.Qty, L2.Qty, L1.Qty)
FROM
  yourTable   AS L1
OUTER APPLY
(
  SELECT * FROM yourTable WHERE parentID = L1.ID
  UNION ALL
  SELECT NULL, NULL, NULL
)
  AS L2
OUTER APPLY
(
  SELECT * FROM yourTable WHERE parentID = L2.ID
  UNION ALL
  SELECT NULL, NULL, NULL
)
  AS L3
WHERE
  L1.ParentID IS NULL

您将获得 LOT 行。就在您的示例中，8 个输入行变成了 18 个输出行。 30 万个输入行很容易变成数百万个输出行，具体取决于数据中的重复程度。

具有多个父项的父子层次结构扁平化

Flatten parent child hierarchy with multiple parents

sql

sql-server

tsql

hierarchy

hierarchyid