sql - MySQL 嵌套集 - 如何查找节点的父节点？

Question

我有您的常规嵌套集层次结构类型设置，其中包含以下列:

表名:

myset

列:

id, name, lft, rgt

有人知道确定节点的父级的查询吗？

我读到了一些地方，在表中添加一个 parent_id 列来跟踪这一点很方便，但这似乎是多余的，而且似乎可能与嵌套的不同步如果在添加/删除/移动集合中的任何内容时查询执行不正确，则设置。

Answer 1

看看this question 。它和你的很相似。我在那里发布了您可能需要的查询。

SELECT title, (SELECT TOP 1 title 
           FROM tree t2 
           WHERE t2.lft < t1.lft AND t2.rgt > t1.rgt    
           ORDER BY t2.rgt-t1.rgt ASC) AS parent
FROM tree t1
ORDER BY rgt-lft DESC

希望有您需要的内容。

如下表:

+-------------+----------------------+-----+-----+
| category_id | name                 | lft | rgt |
+-------------+----------------------+-----+-----+
|           1 | ELECTRONICS          |   1 |  20 |
|           2 | TELEVISIONS          |   2 |   9 |
|           3 | TUBE                 |   3 |   4 |
|           4 | LCD                  |   5 |   6 |
|           5 | PLASMA               |   7 |   8 |
|           6 | PORTABLE ELECTRONICS |  10 |  19 |
|           7 | MP3 PLAYERS          |  11 |  14 |
|           8 | FLASH                |  12 |  13 |
|           9 | CD PLAYERS           |  15 |  16 |
|          10 | 2 WAY RADIOS         |  17 |  18 |

它产生输出:

title                | parent
----------------------------------------------
ELECTRONICS          | NULL
PORTABLE ELECTRONICS | ELECTRONICS
TELEVISIONS          | ELECTRONICS
MP3 PLAYERS          | PORTABLE ELECTRONICS
FLASH                | MP3 PLAYERS
CD PLAYERS           | PORTABLE ELECTRONICS
2 WAY RADIOS         | PORTABLE ELECTRONICS
TUBE                 | TELEVISIONS
LCD                  | TELEVISIONS
PLASMA               | TELEVISIONS