Oracle 中的递归

Question

我在预言中有下表：

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，

Ancestor(arg1, arg2)

这在Oracle中怎么可能？

我正在执行以下操作：

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？

Answer 1

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 仅从 11g 第 2 版开始支持递归 CTE。

在早期版本中，使用 CONNECT BY 子句：

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

Answer 2

Oracle 允许递归查询。
请参阅：http://www.adp-gmbh.ch/ora/sql/connect_by .html

当然，这些通常假设分层数据都在一张表中。将其拆分为单独的表会使事情变得复杂。