获取 MySQL 表中的树路径

2022-01-05 00:00:00 tree mysql

也许在 MySQL 数据库中管理分层数据最简单的方法是 邻接列表模型.也就是说，给每个节点一个父节点:

Perhaps the easiest approach to manage hierarchical data in MySQL databases is the adjacency list model. It is, give to every node a parent:

CREATE TABLE category(
category_id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(20) NOT NULL,
parent INT DEFAULT NULL);

获取父节点很容易，或者即使有最大树深度，也可以使用这个获取整棵树:

It is easy to get the parent node, or even if there is a maximum tree depth, you can get the whole tree using this: 

SELECT CONCAT_WS('/', `t3`.`name`, `t2`.`name`, `t1`.`name`) AS `path`
FROM category AS t1
LEFT JOIN category AS t2 ON t2.parent = t1.category_id
LEFT JOIN category AS t3 ON t3.parent = t2.category_id
LEFT JOIN category AS t4 ON t4.parent = t3.category_id
WHERE t1.name = 'xxxxx';

这在很多情况下就足够了，但是您如何将这个解决方案推广到深度超过 3 个节点的树呢?IE.您可能有类似电子/音频/发射器/FM/摩托罗拉"这样的路径.

That's enough in many cases, but how can you generalize this solution for trees deeper than 3 nodes? I.e. You may have a path like "Electronics/Audio/Transmiter/FM/Motorola".

可以只查询一个吗?

推荐答案

这里有一个简单的非递归存储过程来完成这项工作:

here's a simple non recursive stored procedure that does the job:

drop table if exists employees;
create table employees
(
emp_id smallint unsigned not null auto_increment primary key,
name varchar(255) not null,
boss_id smallint unsigned null,
key (boss_id)
)
engine = innodb;

insert into employees (name, boss_id) values
('f00',null), 
  ('ali later',1), 
  ('megan fox',1), 
      ('jessica alba',3), 
      ('eva longoria',3), 
         ('keira knightley',5), 
            ('liv tyler',6), 
            ('sophie marceau',6);


drop procedure if exists employees_hier;

delimiter #

create procedure employees_hier
(
in p_emp_id smallint unsigned
)
begin

declare v_done tinyint unsigned default(0);
declare v_dpth smallint unsigned default(0);

create temporary table hier(
 boss_id smallint unsigned, 
 emp_id smallint unsigned, 
 depth smallint unsigned
)engine = memory;

insert into hier select boss_id, emp_id, v_dpth from employees where emp_id = p_emp_id;

/* http://dev.mysql.com/doc/refman/5.0/en/temporary-table-problems.html */

create temporary table emps engine=memory select * from hier;

while not v_done do

    if exists( select 1 from employees e inner join hier on e.boss_id = hier.emp_id and hier.depth = v_dpth) then

        insert into hier select e.boss_id, e.emp_id, v_dpth + 1 
            from employees e inner join emps on e.boss_id = emps.emp_id and emps.depth = v_dpth;

        set v_dpth = v_dpth + 1;            

        truncate table emps;
        insert into emps select * from hier where depth = v_dpth;

    else
        set v_done = 1;
    end if;

end while;

select 
 e.emp_id,
 e.name as emp_name,
 p.emp_id as boss_emp_id,
 p.name as boss_name,
 hier.depth
from 
 hier
inner join employees e on hier.emp_id = e.emp_id
left outer join employees p on hier.boss_id = p.emp_id;

drop temporary table if exists hier;
drop temporary table if exists emps;

end #

delimiter ;

-- call this sproc from your php

call employees_hier(1);

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