闭包表结构

将Closure Table翻译成闭包表不知道是否合适，闭包表的思路和物化路径差不多，都是空间换时间，Closure Table，一种更为彻底的全路径结构，分别记录路径上相关结点的全展开形式。能明晰任意两结点关系而无须多余查询，级联删除和结点移动也很方便。但是它的存储开销会大一些，除了表示结点的Meta信息，还需要一张专用的关系表。

以下图举例数据举例：

tree

创建主表：

CREATE TABLE nodeInfo (
node_id INT NOT NULL AUTO_INCREMENT,
node_name VARCHAR (255),
PRIMARY KEY (node_id)
) DEFAULT CHARSET = utf8;

创建关系表：

CREATE TABLE nodeRelationship (
ancestor INT NOT NULL,
descendant INT NOT NULL,
distance INT NOT NULL,
PRIMARY KEY (ancestor, descendant)
) DEFAULT CHARSET = utf8;
其中

Ancestor代表祖先节点
Descendant代表后代节点
Distance 祖先距离后代的距离
添加数据（创建存储过程）

CREATE DEFINER = root@localhost PROCEDURE AddNode(_parent_name varchar(255),_node_name varchar(255))
BEGIN
DECLARE _ancestor INT;
DECLARE _descendant INT;
DECLARE _parent INT;
IF NOT EXISTS(SELECT node_id From nodeinfo WHERE node_name = _node_name)
THEN
INSERT INTO nodeinfo (node_name) VALUES(_node_name);
SET _descendant = (SELECT node_id FROM nodeinfo WHERE node_name = _node_name);
INSERT INTO noderelationship (ancestor,descendant,distance) VALUES(_descendant,_descendant,0);
IF EXISTS (SELECT node_id FROM nodeinfo WHERE node_name = _parent_name)
THEN
SET _parent = (SELECT node_id FROM nodeinfo WHERE node_name = _parent_name);
INSERT INTO noderelationship (ancestor,descendant,distance) SELECT ancestor,_descendant,distance+1 from noderelationship where descendant = _parent;
END IF;
END IF;
END;
完成后2张表的数据大致是这样的：（注意：每个节点都有一条到其本身的记录。）

Closure-Table-1

Closure-Table-2

查询Fruit下所有的子节点：

SELECT
n3.node_name
FROM
nodeinfo n1
INNER JOIN noderelationship n2 ON n1.node_id = n2.ancestor
INNER JOIN nodeinfo n3 ON n2.descendant = n3.node_id
WHERE
n1.node_name = ‘Fruit’
AND n2.distance != 0
查询Fruit下直属子节点：

SELECT
n3.node_name
FROM
nodeinfo n1
INNER JOIN noderelationship n2 ON n1.node_id = n2.ancestor
INNER JOIN nodeinfo n3 ON n2.descendant = n3.node_id
WHERE
n1.node_name = ‘Fruit’
AND n2.distance = 1
查询Fruit所处的层级：

SELECT
n2.*, n3.node_name
FROM
nodeinfo n1
INNER JOIN noderelationship n2 ON n1.node_id = n2.descendant
INNER JOIN nodeinfo n3 ON n2.ancestor = n3.node_id
WHERE
n1.node_name = ‘Fruit’
ORDER BY
n2.distance DESC
另外要删除节点也非常的简单，这里就不再做过多的阐述。