在邻接列表中查找后代深度

Question

问题

示例表

+-------------+----------------------+--------+
| category_id | name                 | parent |
+-------------+----------------------+--------+
|           1 | ELECTRONICS          |   NULL |
|           2 | TELEVISIONS          |      1 |
|           3 | TUBE                 |      2 |
|           4 | LCD                  |      2 |
|           5 | PLASMA               |      2 |
|           6 | PORTABLE ELECTRONICS |      1 |
|           7 | MP3 PLAYERS          |      6 |
|           8 | FLASH                |      7 |
|           9 | CD PLAYERS           |      6 |
|          10 | 2 WAY RADIOS         |      6 |
+-------------+----------------------+--------+

鉴于上面的示例表，我认为在 Oracle 中我应该能够沿着“SELECT ... CONNECT BY”的行编写 SQL 来查找给定 id 的级别。例如，“MP3 播放器”的 LEVEL 为 3。

示例借自 管理层次结构MySQL中的数据

解决方案

SELECT MAX(level) "LEVEL"
FROM TEST_TABLE
START WITH category_id = 7 -- MP3 Players category_id
CONNECT BY category_id = PRIOR parent
ORDER BY LEVEL DESC

Answer 1

您可以使用level伪列来获取当前行的“深度”。考虑以下陈述：

SELECT category_id, name, level,
 PRIOR name as parent_category
FROM test_table
START WITH parent is null
CONNECT BY PRIOR category_id = parent