Oracle 中的递归

2021-12-05 00:00:00 递归 oracle

我在 oracle 中有下表:

I have the following table in an oracle:

Parent(arg1, arg2)

并且我想要关系父级的传递闭包.也就是说，我想要下表

and I want the transitive closure of the relation parent. That is, I want the following table

Ancestor(arg1, arg2)

这在 Oracle 中怎么可能?

How is this possible in Oracle?

我正在做以下事情:

WITH Ancestor(arg1, arg2)  AS (

  SELECT p.arg1, p.arg2 from parent p
  UNION
  SELECT p.arg1 , a.arg2 from parent p,  Ancestor a 
  WHERE p.arg2 = a.arg1

)

SELECT DISTINCT * FROM Ancestor;

我收到错误

*Cause:    column aliasing in WITH clause is not supported yet
*Action:   specify aliasing in defintion subquery and retry
Error at Line: 1 Column: 20

如何在没有列别名的情况下解决此问题?

How can I solve this without column aliasing?

推荐答案

WITH    Ancestor(arg1, arg2) AS
        (
        SELECT  p.arg1, p.arg2
        FROM    parent p
        WHERE   arg2 NOT IN
        (
            SELECT  arg1
            FROM    parent
        )

        UNION ALL

        SELECT  p.arg1, a.arg2
        FROM    Ancestor a 
        JOIN    parent p
        ON      p.arg2 = a.arg1
        )
SELECT  *
FROM    Ancestor

Oracle 自 11g Release 2 起仅支持递归 CTE.

Oracle only supports recursive CTE since 11g Release 2.

在早期版本中，使用CONNECT BY 子句:

In earlier versions, use CONNECT BY clause:

SELECT  arg1, CONNECT_BY_ROOT arg2
FROM    parent
START WITH
        arg2 NOT IN
        (
        SELECT  arg1
        FROM    parent
        )
CONNECT BY
        arg2 = PRIOR arg1

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