php树形构造的算法（二）[网站编程]

1 Food 18
|
+---------------------------------------+
| |
2 Fruit 11 12 Meat 17
| |
+------------------------+ +---------------------+
| | | |
3 Red 6 7 Yellow 10 13 Beef 14 15 Pork 16
| |
4 Cherry 5 8 Banana 9

　　这样整个树状构造可以通过左右值来存储到数据库中.持续之前,我们看一看下面整理过的数据表.


+-----------------------+-----+-----+
| parent | name | lft | rgt |
+-----------------------+-----+-----+
| | Food | 1 | 18 |
| Food | Fruit | 2 | 11 |
| Fruit | Red | 3 | 6 |
| Red | Cherry | 4 | 5 |
| Fruit | Yellow | 7 | 10 |
| Yellow | Banana | 8 | 9 |
| Food | Meat | 12 | 17 |
| Meat | Beef | 13 | 14 |
| Meat | Pork | 15 | 16 |
+-----------------------+-----+-----+
 

　　注意:由于"left"和"right"在 SQL中有特别的意义,所以我们需求用"lft"和"rgt"来表示左右字段. 别的这种构造中不再需求"parent"字段来表示树状构造.也就是 说下面这样的表构造就充足了.
 

+------------+-----+-----+
| name | lft | rgt |
+------------+-----+-----+
| Food | 1 | 18 |
| Fruit | 2 | 11 |
| Red | 3 | 6 |
| Cherry | 4 | 5 |
| Yellow | 7 | 10 |
| Banana | 8 | 9 |
| Meat | 12 | 17 |
| Beef | 13 | 14 |
| Pork | 15 | 16 |
+------------+-----+-----+
 

　　好了我们目前可以从数据库中获得数据了,比方我们需求得到"Fruit"项下的全部全部节点便可以这样写查询语句: SELECT * FROM tree WHERE lft BETWEEN 2 AND 11; 这个查询得到了以下的后果.

+------------+-----+-----+
| name | lft | rgt |
+------------+-----+-----+
| Fruit | 2 | 11 |
| Red | 3 | 6 |
| Cherry | 4 | 5 |
| Yellow | 7 | 10 |
| Banana | 8 | 9 |
+------------+-----+-----+

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