计算树中值的总和（递归查询）

Question

我在员工表（id、name、parentid）中有树结构，这个表可以嵌套。employees 与另一个表 Sales 是一对多的关系，其中包含列（id、employeeid、数量）。每个员工都有销售数量。我想计算每个员工以及儿童员工的数量总和。为了更清楚，我写了一些代码。

DECLARE @Employees TABLE(ID INT, Name NVARCHAR(100), ParentID INT);
DECLARE @Sales TABLE(ID INT, EmployeeID INT, Quantity INT);    

INSERT INTO @Employees(ID, Name, ParentID)VALUES
(1,N'Employee1', NULL),
(2,N'Employee2', 1),
(3,N'Employee3', 2),
(4,N'Employee4', NULL),
(5,N'Employee5', 4),
(6, N'Employee6', 5)

INSERT INTO @Sales(ID, EmployeeID, Quantity)VALUES
(1,1,4),
(2,1,2),
(3,2,3),
(4,3,2),
(5,3,7),
(6,5,8),
(7,5,3),
(8,6,2)

我加入了这个表格，看起来像这样：

这是我的查询

;WITH cte 
AS
(
  SELECT e.ID, e.Name, e.ParentID FROM @Employees e
  WHERE e.ParentID IS NULL
  UNION ALL
  SELECT  e.ID, e.Name, e.ParentID  FROM @Employees e
    INNER JOIN cte c ON c.ID = e.ParentID
)
SELECT
     c.ID
    ,c.Name
    ,c.ParentID
    ,ISNULL(SUM(s.Quantity), 0) AS ParentSumSales
    ,ISNULL(LEAD(SUM(s.Quantity)) OVER(ORDER BY c.ID), 0) AS ChildSumSales
FROM cte c
    LEFT JOIN @Sales s ON s.EmployeeID = c.ID
GROUP BY c.ID, c.Name, c.ParentID

查询返回这个结果：

但这不正确，我想得到这样的数据：

ID     Name        ParentSumSales    ChildSumSales
---    ---------   -------------     -------------
1      Employee1   6                 12
2      Employee2   3                 9   
3      Employee3   9                 0
4      Employee4   0                 13
5      Employee5   11                2
6      Employee6   2                 0

Answer 1

如果您的“Employees”表偶尔发生变化，我建议您实施Nested set model。写作会更复杂，但阅读会更简单、更快捷。

Answer 2

您使用LEAD 的尝试将不起作用，因为它不会对所有先前的级别求和，并且它的 ID 必须是连续的。

首先展开每个员工的完整层次结构，以便每个员工在每个层次结构级别都包含一次：

;WITH cte 
AS
(
  SELECT e.ID, e.Name, e.ID as sub_ID 
  FROM @Employees e
  -- no WHERE-condition to get all employees
  UNION ALL
  SELECT 
     c.ID, c.Name -- keep the initial employee
     ,e.ID as sub_ID
  FROM @Employees e
    INNER JOIN cte c ON c.sub_ID = e.ParentID
)

SELECT 
     c.ID
    ,c.Name
    -- parent level
    ,sum(case when c.id =  s.EmployeeID then s.Quantity else 0 end) AS ParentSumSales
    -- child level
    ,sum(case when c.id <> s.EmployeeID then s.Quantity else 0 end) AS ChildSumSales
FROM cte c
LEFT JOIN @Sales as s
ON s.EmployeeID = c.sub_ID
group by c.Name, c.id