树形结构与关系数据库之闭包表

闭包表记录了树中所有节点的关系，不仅仅只是直接父子关系，它需要使用2张表，除了节点表本身之外，还需要使用1张表来存储节祖先点和后代节点之间的关系（同时增加一行节点指向自身）,
并且根据需要，可以增加一个字段，表示深度。因此这种方法数据量很多。设计的表结构如下：

create table `node` (
  `id` int(10) not null,
  `name` varchar(50) default null,
  primary key (`id`)
) engine=innodb default charset=utf8;

create table `tree_path` (
  `anc` int(10) not null comment '祖先节点',
  `des` int(10) not null comment '子孙节点',
  `pc` int(1) default null comment '是否为父子节点 1/0',
  primary key (`anc`,`des`)
) engine=innodb default charset=utf8;

-- 示例树
-- root(0)
--     |
--     a(1)
--     |___a1(2)
--     |___a2(3)
--     b(4)
--     |___b1(5)
--     |___b2(6)
--     |___c(7)
--         |___c1(8)
--         |___d(9)
--             |___e(10)


insert into node(id,name) values (0,'root');
insert into node(id,name) values (1,'a');
insert into node(id,name) values (2,'a1');
insert into node(id,name) values (3,'a2');
insert into node(id,name) values (4,'b');
insert into node(id,name) values (5,'b1');
insert into node(id,name) values (6,'b2');
insert into node(id,name) values (7,'c');
insert into node(id,name) values (8,'c1');
insert into node(id,name) values (9,'d');
insert into node(id,name) values (10,'e');

 
insert into tree_path(anc,des,pc) values (0,1,1);
insert into tree_path(anc,des,pc) values (0,2,0);
insert into tree_path(anc,des,pc) values (0,3,0);
insert into tree_path(anc,des,pc) values (0,4,1);
insert into tree_path(anc,des,pc) values (0,5,0);
insert into tree_path(anc,des,pc) values (0,6,0);
insert into tree_path(anc,des,pc) values (0,7,0);
insert into tree_path(anc,des,pc) values (0,8,0);
insert into tree_path(anc,des,pc) values (0,9,0);
insert into tree_path(anc,des,pc) values (0,10,0);

insert into tree_path(anc,des,pc) values (1,1,0);
insert into tree_path(anc,des,pc) values (2,2,0);
insert into tree_path(anc,des,pc) values (3,3,0);
insert into tree_path(anc,des,pc) values (4,4,0);
insert into tree_path(anc,des,pc) values (5,5,0);
insert into tree_path(anc,des,pc) values (6,6,0);
insert into tree_path(anc,des,pc) values (7,7,0);
insert into tree_path(anc,des,pc) values (8,8,0);
insert into tree_path(anc,des,pc) values (9,9,0);
insert into tree_path(anc,des,pc) values (10,10,0);

insert into tree_path(anc,des,pc) values (1,2,1);
insert into tree_path(anc,des,pc) values (1,3,1);

insert into tree_path(anc,des,pc) values (4,5,1);
insert into tree_path(anc,des,pc) values (4,6,1);
insert into tree_path(anc,des,pc) values (4,7,1);
insert into tree_path(anc,des,pc) values (4,8,0);
insert into tree_path(anc,des,pc) values (4,9,0);
insert into tree_path(anc,des,pc) values (4,10,0);

insert into tree_path(anc,des,pc) values (7,8,1);
insert into tree_path(anc,des,pc) values (7,9,1);
insert into tree_path(anc,des,pc) values (7,10,0);

insert into tree_path(anc,des,pc) values (9,10,1);

删除子树
假设要删除子树#7

delete from tree_path
where tree_path.des in (select t.des from tree_path t where t.anc=7)

移动子树
假设我们要把子树#7从节点#4移动到节点#1
1.分离子树,删除子树节点与其祖先的关系
delete from tree_path where tree_path.anc=7

2.将上一步分离出的子树用笛卡尔积嫁接到#1下
select
    super.anc,
    sub.des,
    case
        when
            super.anc=1 and sub.des=7 then 1
        else 0
    end pc
from
    tree_path super
    cross join
    tree_path sub
where
    super.des=1 and sub.anc=7
    
查询树形结构
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