sql - 如何在代表层次结构的表中找到最高记录（在 TSQL 中）？

Question

想象一个如下表：

表：人

字段： ID、FullName、ParentID

ParentID 再次引用 Person 表中的 ID。

问题： 对于上面给出的示例，我如何在 TSQL 中查询以找到 ID = 7 的 Person 的最高父级？

Answer 1

您将使用公用表表达式并执行递归查询，直到找到最顶层的父项，如下所示：

DECLARE @id INT
SET @id = 5 

CREATE TABLE #tmp (id INT , ParentId INT)
INSERT INTO #tmp VALUES(1,0)
INSERT INTO #tmp VALUES(2,1)
INSERT INTO #tmp VALUES(3,2);
INSERT INTO #tmp VALUES(4, 3);
INSERT INTO #tmp VALUES(5,4);

    WITH parent AS
    (
        SELECT id, parentId  from #tmp WHERE id = @id
        UNION ALL 
        SELECT t.id, t.parentId FROM parent
        INNER JOIN #tmp t ON t.id =  parent.parentid
    )

    SELECT TOP 1 id FROM  parent
    order by id asc

DROP TABLE #tmp

Answer 2

如果想测试那个查询应该没问题！

WITH  abcd
            AS (
                  -- anchor
                SELECT  id, FullName, ParentID,
                        FullName AS "Path"
                FROM    Person
                WHERE   ParentId IS NULL
                UNION ALL
                  --recursive member
                SELECT  p.id, p.FullName, p.ParentID,
                        CAST((a.path + '/' + p.FullName) AS VARCHAR(1000)) AS "Path"
                FROM    Person AS p
                        JOIN abcd AS a
                          ON p.ParentId = a.id
               )
    SELECT * FROM abcd