java - tree形结构的Nested Set 数据如何转成Adjacency List的

Answer 1

之前想简单了，需要多一层子查询，修改如下：

SELECT node.name, parent.id AS pid
FROM `nested` as node
  LEFT OUTER JOIN `nested` AS parent
    ON parent.`left` = (
      SELECT MAX(parents.`left`)
      FROM nested AS parents
      WHERE node.`left` > parents.`left` AND node.`left` < parents.`right`
    )
ORDER BY node.id;

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参考我之前翻译整理的 https://segmentfault.com/a/11... 中《获取整棵树》一节的第二个例子，主要的修改是将 (COUNT(parent.name) - 1) AS depth 改成 parent.id 就可以得到类似邻接表的形态。