使用 CTE 获取所有父级的 Id，包括根的 Id

Question

从 EmployeeId 8 我想得到他所有的父母 EmployeeId，这些是 EmployeeId 的 7,5,3,2,1

CREATE TABLE EmployeeTree(
    EmployeeId int,
        EmployeeName nvarchar(100),
        EmployeeType nvarchar(40),
    EmployeeParentId int 
)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (1, 'Mickey Mouse', 'CEO', NULL)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (2, 'Minnie Mouse', 'President', 1)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (3, 'Donald Duck', 'Division Head', 2)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (4, 'Daffy Duck', 'Division Head', 2)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (5, 'Scrooge McDuck', 'Department Head', 3)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (6, 'Huey McDuck', 'Team Lead', 5)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (7, 'Dewey McDuck', 'Team Lead', 5)

INSERT INTO EmployeeTree (EmployeeId, EmployeeName, EmployeeType, EmployeeParentId)
VALUES (8, 'Louie McDuck', 'Team Member', 7)

使用这段代码我遇到了递归问题：

DECLARE @EmployeeId INT
SET @EmployeeId = 8;


WITH x(Id) AS (SELECT @EmployeeId UNION ALL SELECT dbo.EmployeeTree.EmployeeId 
 FROM dbo.EmployeeTree INNER JOIN x ON EmployeeTree.EmployeeId = x.Id )
Select * FROM x JOIN dbo.EmployeeTree as e ON e.EmployeeParentId = x.Id

我必须在我的 CTE 中更正什么，才能获得employeeId 8 的所有父员工ID？

Answer 1

您可以使用此 CTE 查询来实现。请注意，锚查询还会从您的源表中进行选择，并且在每次迭代中都会返回员工 ID 和父 ID，以便每次都可以连接父级。

DECLARE @EmployeeId INT
SET @EmployeeId = 8;

WITH x AS (
    SELECT EmployeeId, EmployeeParentId
    FROM dbo.EmployeeTree 
    WHERE EmployeeId = @EmployeeId 

    UNION ALL 

    SELECT dbo.EmployeeTree.EmployeeId, dbo.EmployeeTree.EmployeeParentId
    FROM dbo.EmployeeTree
    INNER JOIN x ON EmployeeTree.EmployeeId = x.EmployeeParentId )

Select EmployeeId FROM x
where EmployeeId <> @EmployeeId