Home Database Mysql Tutorial mysql父子结构排序_MySQL

mysql父子结构排序_MySQL

Jun 01, 2016 pm 01:15 PM
m database

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
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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) DETERMINISTICbegin  DECLARE 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 ;
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2. 调用函数得到的便是排完序的结果
SELECT * FROM category ORDER BY getPriority(ID);
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☆ 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。

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