Question

我有一个带有列的树结构表： ID，父名。给定树A-> B-> C，我如何根据C的ID获得最顶级的父母A的身份证？特别是如何用“with recursive”编写SQL？谢谢！

Answer 1

要实现递归查询，您需要Common Table Expression（CTE）。此查询计算所有父节点的祖先。由于我们只想要顶级，我们选择level = 0。

WITH RECURSIVE Ancestors AS
(
   SELECT id, parent, 0 AS level FROM YourTable WHERE parent IS NULL
   UNION ALL
   SELECT child.id, child.parent, level+1 FROM YourTable child INNER JOIN
      Ancestors p ON p.id=child.parent

)
SELECT * FROM Ancestors WHERE a.level=0 AND a.id=C

如果要获取所有数据，请在ID上使用内部联接，例如

SELECT YourTable.* FROM Ancestors a WHERE a.level=0 AND a.id=C
   INNER JOIN YourTable ON YourTable.id = a.id

Answer 2

WITH    RECURSIVE q AS
        (
        SELECT  m
        FROM    mytable m
        WHERE   id = 'C'
        UNION ALL
        SELECT  m
        FROM    q
        JOIN    mytable m
        ON      m.id = q.parent
        )
SELECT  (m).*
FROM    q
WHERE   (m).parent IS NULL

如何获得PostgreSQL中最顶级的父级

2 个答案: