查询一棵树的数据库表示(MySQL) [英] Querying a database representation of a tree (MySQL)

问题描述

我有两个表，一个包含节点，第二个包含它们之间的关系，如下所示:

I have two tables, one that contains nodes and second that contains the relationships between them like so:

表A(命名节点)

NodeID | NodeName 
 100   |  Name 1
 101   |  Name 2
 102   |  Name 3

表 B(命名关系)

NodeParent | NodeChild
  100      |    101
  101      |    102

我需要执行一个查询，该查询需要找出哪些节点是孤立节点(它们不在关系表中).如何同时搜索 NodeParent 和 NodeChild?

I need to execute a query that needs to find which nodes are orphans (they are not in the Relationship table). How can I search through NodeParent and NodeChild at the same time?

推荐答案

SELECT 
  n.NodeID 
FROM 
  Node AS n 
LEFT JOIN 
  Relationship AS r
ON
  n.NodeID = r.NodeChild
WHERE
  r.NodeChild IS NULL

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