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HomeDatabaseMysql Tutorialmysql 父子结构排序_MySQL

项目中经常会遇到父子结构显示的问题,不同的数据库有不同的写的方式,比如SqlServer中用with union 实现,而Mysql则没有这么方便的语句。

如下category表,食品有pizaa,buger,coffee,而pizza又分了加cheese几种,如何将他们的父子结构表现出来呢?

CREATE TABLE category(	id INT(10),	parent_id INT(10),	name VARCHAR(50));INSERT INTO category (id, parent_id, name) VALUES(1, 0, 'pizza'),		--node 1(2, 0, 'burger'),	 --node 2(3, 0, 'coffee'),	 --node 3(4, 1, 'piperoni'),	 --node 1.1(5, 1, 'cheese'),	 --node 1.2(6, 1, 'vegetariana'),--node 1.3(7, 5, 'extra cheese'); --node 1.2.1

stackoverflow上一个人给了一个很好的解决方案:

1. 创建一个函数

delimiter ~DROP FUNCTION getPriority~CREATE FUNCTION getPriority (inID INT) RETURNS VARCHAR(255) DETERMINISTICbeginDECLARE gParentID INT DEFAULT 0;DECLARE gPriority VARCHAR(255) DEFAULT '';SET gPriority = inID;SELECT parent_id INTO gParentID FROM category WHERE ID = inID;WHILE gParentID > 0 DO/*0为根*/SET gPriority = CONCAT(gParentID, '.', gPriority);SELECT parent_id INTO gParentID FROM category WHERE ID = gParentID;END WHILE;RETURN gPriority;end~delimiter ;
2. 调用函数得到的便是排完序的结果
SELECT * FROM category ORDER BY getPriority(ID);

☆ getPriority 这个函数的限制条件是:所有数据追溯上去必须有唯一的祖先。从树结构来看,不能有多棵树。

来源:http://stackoverflow.com/questions/14890204/order-sql-tree-hierarchy

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