从MySQL中的分层数据生成基于深度的树(无CTE)

Question

嗨很多天我一直在研究MySQL中的这个问题,但我无法弄明白.你们有什么建议吗？

基本上,我有一个类别表,其域名包括:id,name(类别名称)和parent(类别的父ID).

示例数据:

1  Fruit        0
2  Apple        1
3  pear         1
4  FujiApple    2
5  AusApple     2
6  SydneyAPPLE  5
....

有许多级别,可能超过3个级别.我想创建一个sql查询,根据他的层次结构对数据进行分组:parent> child> grandchild>等.

它应该输出树结构,如下所示:

1 Fruit 0
 ^ 2 Apple 1
   ^ 4 FujiApple 2
   - 5 AusApple 2
     ^ 6 SydneyApple 5
 - 3 pear 1

我可以使用单个SQL查询执行此操作吗？我尝试过并且确实有效的替代方案如下:

SELECT * FROM category WHERE parent=0

在此之后,我再次遍历数据,并选择parent = id的行.这似乎是一个糟糕的解决方案.因为它是mySQL,所以不能使用CTE.

Answer 1

如果您使用存储过程,您可以在从php到mysql的单个调用中执行此操作:

示例调用

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)


$sql = sprintf("call category_hier(%d)", $id);

希望这可以帮助 :)

完整的脚本

测试表结构:

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;

测试数据:

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

程序:

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;

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

create temporary table tmp engine=memory select * from hier;

while not v_done do

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

        insert into hier 
            select p.parent_cat_id, p.cat_id, v_depth + 1 from categories p 
            inner join tmp on p.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 
 p.cat_id,
 p.name as category_name,
 b.cat_id as parent_cat_id,
 b.name as parent_category_name,
 hier.depth
from 
 hier
inner join categories p on hier.cat_id = p.cat_id
left outer join categories b on hier.parent_cat_id = b.cat_id
order by
 hier.depth, hier.cat_id;

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

end #

试运行:

delimiter ;

call category_hier(1);

call category_hier(2);

使用Yahoo geoplanet进行的一些性能测试会放置数据

drop table if exists geoplanet_places;
create table geoplanet_places
(
woe_id int unsigned not null,
iso_code  varchar(3) not null,
name varchar(255) not null,
lang varchar(8) not null,
place_type varchar(32) not null,
parent_woe_id int unsigned not null,
primary key (woe_id),
key (parent_woe_id)
)
engine=innodb;

mysql> select count(*) from geoplanet_places;
+----------+
| count(*) |
+----------+
|  5653967 |
+----------+

这样表中的560万行(地方)让我们看看从php调用的邻接列表实现/存储过程是如何处理的.

     1 records fetched with max depth 0 in 0.001921 secs
   250 records fetched with max depth 1 in 0.004883 secs
   515 records fetched with max depth 1 in 0.006552 secs
   822 records fetched with max depth 1 in 0.009568 secs
   918 records fetched with max depth 1 in 0.009689 secs
  1346 records fetched with max depth 1 in 0.040453 secs
  5901 records fetched with max depth 2 in 0.219246 secs
  6817 records fetched with max depth 1 in 0.152841 secs
  8621 records fetched with max depth 3 in 0.096665 secs
 18098 records fetched with max depth 3 in 0.580223 secs
238007 records fetched with max depth 4 in 2.003213 secs

总的来说,我对这些冷运行时非常满意,因为我甚至不会考虑将数万行数据返回到我的前端,而是宁愿构建树,每次调用只动态获取几个级别.哦,只是因为你认为innodb比myisam慢 - 我测试的myisam实现的速度是所有计数的两倍.

更多内容:http://pastie.org/1672733

希望这可以帮助 :)

Answer 2

在RDBMS中存储分层数据有两种常用方法:邻接列表(您正在使用)和嵌套集.关于在MySQL中管理分层数据中的这些备选方案,有一个非常好的文章.您只能使用嵌套集模型在单个查询中执行所需操作.但是,嵌套集模型使更新层次结构更加有效,因此您需要根据操作要求考虑权衡.