Question

我有这张桌子，

    Parenttbl
ID   Name   ParentID
---------------------
1    Mary    Null
2    Jane    1
3    Jenny   2
4    Jessa   3

我想创建一个从子节点循环到父节点的查询。例如，如果我给出4号id，它将返回3,2,1，Null（从jessa到mary），直到它发现父id为Null。到目前为止，我有这个问题：

SELECT fc2.ID
FROM Parenttbl as fc1
LEFT JOIN Parenttbl as fc2
ON fc1.ParentID = fc2.ID
WHERE fc1.ID = 6

我打算使用while循环。我怎样才能做到这一点？提前致谢。

Answer 1

您可以使用WITH Common Table Expressions

WITH Hierarchy AS ( 
    SELECT ID,ParentID
    FROM People
    WHERE ID = 4 
    UNION ALL 
    SELECT p.ID, p.ParentID 
    FROM People p
    JOIN Hierarchy h ON h.ParentID = p.ID 
) 
SELECT ID FROM Hierarchy

Answer 2

使用递归查询。像这样：

WITH ParentOf (parentid, name, id, parentlevel)
AS
(
-- Anchor query
    SELECT parentid, name, id, 1 as parentLevel
    FROM parenttbl
    WHERE parenttbl.id = 4
    UNION ALL
-- Recursive query
    SELECT p.parentid, p.name, p.id, parentlevel +1  
    FROM parenttbl p
    INNER JOIN ParentOf  
        ON p.Id = ParentOf.parentid
)
-- Statement that executes the CTE
SELECT ParentId, name, id, parentlevel
FROM ParentOf;

sqlfiddle

Answer 3

最简单的解决方案是使用Recursive CTE覆盖任何类型的循环或游标方法

with cte as
(
    select * from parenttbl
    where id = 4
    union all
    select p.* from parenttbl p 
    inner join cte c on p.id <= c.parentid
) 
select id, name, parentid from cte
group by id, name, parentid

Self Referenc循环MSSQL

3 个答案: