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树形结构数据存储方案(三):闭包表

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:

创建主表:

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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:

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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)

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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。)

查询Fruit下所有的子节点:

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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

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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:

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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。
参考链接:

https://coderwall.com/p/lixing/closure-tables-for-browsing-trees-in-sql

转自https://www.biaodianfu.com/closure-table.html

作者:标点符

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