sql - 如何从 SQL 表中的父节点获取子节点？

Question

假设我的数据库中有以下分层表示：

A
|_B_C
|_D

然后我想从A（或B）获取子节点。反之亦然，我想从给定的子节点获取父节点？<>

CREATE TABLE tbl (
   Node HierarchyID PRIMARY KEY CLUSTERED,
   NodeLevel AS Node.GetLevel(),
   ID INT UNIQUE NOT NULL,
   Name VARCHAR(50) NOT NULL
 ) 

插入根：

INSERT INTO tbl (Node, ID, Name)
   VALUES (HierarchyId::GetRoot(), 1, 'A') 

孩子乙

DECLARE @parent HierarchyId = HierarchyId::GetRoot()
INSERT INTO tbl (Node,ID,Name) VALUES (@parent.GetDescendant(NULL,NULL),2,'B')

Answer 1

select @child = node from tbl where id = 2;
-- get immediate ancestor
select * from dbo.tbl where Node = @child.GetAncestor(1);

-- get immediate children
select
    *
from
    dbo.tbl
where
    Node.IsDescendantOf(@parent) = 1 and 
    Node.GetLevel() = @parent.GetLevel() + 1;