我正在试图查询一个具有分层类别数据（用于cms）的表，这也与我的帖子数据和我的post2cat表的多对多类型关系有关。具体来说，我的问题是如何获得属于特定类别ID的任何子类别（不限于直接后代但可以是n级深度）的所有帖子？这是我的表格：
'类别'表：
+-----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(45) | YES | | NULL | |
| parent_id | int(11) | YES | MUL | 0 | |
+-----------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
'post2cat'表：
+---------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+-------+
| post_id | int(11) | NO | MUL | NULL | |
| cat_id | int(11) | NO | MUL | NULL | |
+---------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
'posts'表：
+---------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| title | varchar(256) | NO | | NULL | |
| content | text | NO | | NULL | |
| end_date | datetime | NO | | NULL | |
| format_id | int(11) | NO | | NULL | |
| featured | int(1) | NO | | NULL | |
| status | int(3) | NO | | NULL | |
| publish_date | datetime | NO | | NULL | |
| date_created | datetime | NO | | NULL | |
| date_modified | datetime | NO | | NULL | |
+---------------+--------------+------+-----+---------+----------------+
post_id名称说明
post2cat
答案 0 :(得分：4)
使用MySQL中的SQL，将树提取到任意深度 n 是一项挑战（参见：Managing Hierarchical Data in MySQL和Hierarchical Queries in MySQL）。
如果您正在处理一个小数据集，那么最有意义的是从数据库中选择所有类别，然后使用脚本语言构建树。然后可以遍历树以查找父节点和父节点的子节点，然后可以使用它来使用连接查询数据库中的帖子。
答案 1 :(得分：1)
也许有更好的方法，但这是一个想法：
CREATE VIEW subcategories AS
( SELECT 0 AS level
, cat_0.id AS cat_id
, cat_0.id AS subcat_id
FROM categories cat_0
UNION ALL
SELECT 1 AS level
, cat_0.id AS cat_id
, cat_1.id AS subcat_id
FROM categories cat_0
JOIN categories cat_1
ON cat_0.id = cat_1.parent_id
UNION ALL
SELECT 2 AS level
, cat_0.id AS cat_id
, cat_2.id AS subcat_id
FROM categories cat_0
JOIN categories cat_1
ON cat_0.id = cat_1.parent_id
JOIN categories cat_2
ON cat_1.id = cat_2.parent_id
UNION ALL
SELECT 3 AS level
, cat_0.id AS cat_id
, cat_3.id AS subcat_id
FROM categories cat_0
JOIN categories cat_1
ON cat_0.id = cat_1.parent_id
JOIN categories cat_2
ON cat_1.id = cat_2.parent_id
JOIN categories cat_3
ON cat_2.id = cat_3.parent_id
) ;
然后，使用上面的内容：
SELECT sub.subcat_id
, sub.level
, p.post_id
, p.title
FROM subcategories sub
JOIN post2cat p2c
ON sub.subcat_id = p2c.cat_id
JOIN posts p
ON p2c.post_id = p.id
WHERE sub.cat_id = CAT_ID <--- the category id you want to search for
答案 2 :(得分：0)
以下存储过程应该提供一个良好的起点或提供一些灵感。
希望有所帮助：）
示例调用
您可以按如下方式从php调用存储过程：
$result = $conn->query(sprintf("call category_hier(%d)", 1));
或者从mysql命令行：
mysql> call category_hier(1);
+--------+---------------+---------------+----------------------+-------+
| cat_id | category_name | parent_cat_id | parent_category_name | depth |
+--------+---------------+---------------+----------------------+-------+
| 1 | Location | NULL | NULL | 0 |
| 3 | USA | 1 | Location | 1 |
| 4 | Illinois | 3 | USA | 2 |
| 5 | Chicago | 3 | USA | 2 |
+--------+---------------+---------------+----------------------+-------+
4 rows in set (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;
drop temporary table if exists hier;
drop temporary table if exists tmp;
end #
delimiter ;
call category_hier(1);
call category_hier(2);