对表中分层数据的所有子节点进行计数 - Count all child nodes of hierarchical data in a table

我想使用邻接模型（父子键）计算表中维护的任何树结构级别下所有子节点的数量。表结构和数据如下所示：

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 具有以下子项和孙子结构：

乙
- E
  - H
  - 我
    - J
- F
  - K

现在，如果您想计算"B 的所有子节点"，我的答案应该是 6。

任何基于纯SQL查询的解决方案都将有很大帮助。或者mysql/php也可以工作。

谢谢！

存储数据的方式不允许通过简单的查询来获取子项总数。但请看一下：

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

像这样的查询是可能的。

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'

将*_num_rows和*_fetch_array替换为您正在使用的 SQL 扩展的任何函数。这不会像纯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参数，但您可以根据需要执行查询。

可以使用非递归存储过程相当简单地完成，如下所示：

示例调用

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)

完整脚本

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);

您可以轻松调整此示例以满足您的要求。

希望对:)有所帮助