统计表中分层数据的所有子节点

Question

我想统计在使用邻接模型（父 - 子键）的表中维护的任何级别的树结构下的所有子节点的数量。表结构和数据看起来像这样：

id - item- parentid  
1 - A - 
2 - B - 1 
3 - C - 1 
4 - D - 2 
5 - E - 2 
6 - F - 3 
7 - G - 3 
8 - H - 5 
9 - I - 5 
10 - J - 9 
11 - K - 4 

例如B已经以下子和大子结构：

• 乙
  • Ë
    • ħ
    • 我
      • Ĵ
  • ˚F
    • ķ

现在，如果要统计 “B的所有子节点的” 我的答案应该是6

任何基于纯SQL查询的解决方案都会非常有帮助。或者mysql/php也可以。

谢谢！

Answer 1

您存储数据的方式不允许使用简单的查询来获取总子数。但是看看：

http://en.wikipedia.org/wiki/Nested_set_model

如果这样的查询将成为可能。

Answer 2

下面是一个基于PHP的解决方案：

function countChildren($startId) { 
    $directDescendents = *_query("SELECT id FROM Table WHERE parentid = ?", array($startId)); 
    $count = *_num_rows($directDescendents); 
    while($row = *_fetch_array($directDescendents)) 
     $count += countChildren($row['id']); 
    return $count; 
} 

$numChildren = countChildren(2); // Number of Children for 'B' 

更换*_num_rows和*_fetch_array与正在使用的任何功能的SQL扩展。这不会像纯粹的SQL解决方案那样高效，但它会起作用。我在函数中查询的方式是假设绑定的参数，但只要你喜欢就执行查询。

Answer 3

可与非递归存储过程相当简单完成如下：

调用示例

mysql> call category_hier(1); 
+--------------+ 
| num_children | 
+--------------+ 
|   3 | 
+--------------+ 
1 row in set (0.00 sec) 

Query OK, 0 rows affected (0.00 sec) 

mysql> call category_hier(2); 
+--------------+ 
| num_children | 
+--------------+ 
|   2 | 
+--------------+ 
1 row in set (0.00 sec) 

Query OK, 0 rows affected (0.00 sec) 

完整剧本

drop table if exists categories; 
create table categories 
(
cat_id smallint unsigned not null auto_increment primary key, 
name varchar(255) not null, 
parent_cat_id smallint unsigned null, 
key (parent_cat_id) 
) 
engine = innodb; 

insert into categories (name, parent_cat_id) values 
('Location',null), 
('Color',null), 
    ('USA',1), 
     ('Illinois',3), 
     ('Chicago',3), 
    ('Black',2), 
    ('Red',2); 


drop procedure if exists category_hier; 
delimiter # 

create procedure category_hier 
(
in p_cat_id smallint unsigned 
) 
begin 

declare v_done tinyint unsigned default 0; 
declare v_depth smallint unsigned default 0; 

create temporary table hier(
parent_cat_id smallint unsigned, 
cat_id smallint unsigned, 
depth smallint unsigned default 0 
)engine = memory; 

insert into hier select parent_cat_id, cat_id, v_depth from categories where cat_id = p_cat_id; 
create temporary table tmp engine=memory select * from hier; 

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

while not v_done do 

    if exists(select 1 from categories c 
     inner join tmp on c.parent_cat_id = tmp.cat_id and tmp.depth = v_depth) then 

     insert into hier select c.parent_cat_id, c.cat_id, v_depth + 1 from categories c 
      inner join tmp on c.parent_cat_id = tmp.cat_id and tmp.depth = v_depth; 

     set v_depth = v_depth + 1;   

     truncate table tmp; 
     insert into tmp select * from hier where depth = v_depth; 

    else 
     set v_done = 1; 
    end if; 

end while; 

/* 
select 
c.cat_id, 
c.name as category_name, 
p.cat_id as parent_cat_id, 
p.name as parent_category_name, 
hier.depth 
from 
hier 
inner join categories c on hier.cat_id = c.cat_id 
left outer join categories p on hier.parent_cat_id = p.cat_id 
order by 
hier.depth; 
*/ 

select count(*) as num_children from hier where parent_cat_id is not null; 

drop temporary table if exists hier; 
drop temporary table if exists tmp; 

end # 

delimiter ; 

call category_hier(1); 

call category_hier(2); 

您可以轻松地适应这个例子来满足你的要求。

希望它能帮助:)