可以通过一个非递归存储过程来相对简单地完成，具体如下：
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;
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 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);
你可以很容易地调整此示例以满足你的需求。
希望这能帮到你 :)
