将一个递归查询的输出重定向到另一个递归查询

Question

我想找到 DAG 的拓扑排序。

CREATE TABLE topo(
v1 int,
v2 int
);

INSERT INTO topo VALUES (1,3),(2,5),(3,4),(4,5),(4,6),(5,7),(6,5),(7,null)

WITH RECURSIVE path(S,d) AS(
 SELECT t1.v1, 0 FROM topo t1 LEFT OUTER JOIN topo AS t2 ON t1.v1=t2.v2 
 WHERE t2.v2 IS NULL
 UNION ALL
 SELECT DISTINCT t1.v2, path.d + 1 FROM path INNER JOIN topo AS t1 ON 
 t1.v1=path.S
)
SELECT S FROM path GROUP BY S ORDER BY MAX(d);

这段代码给出了图的拓扑顺序的输出。现在我想将此输出用于另一个递归查询以找到从一个顶点到另一个顶点的路径。

我可以将此代码生成的输出用于另一个递归查询吗？

Answer 1

添加到您现有的递归 sql 以获取路径：

WITH RECURSIVE path AS(
 select 
   t1.v1 as start,
   t1.v2 as end,  
   CAST(t1.v1 as VARCHAR(30)) as path 
   0 as depth
 from topo t1 
   left outer join topo as t2 on t1.v1=t2.v2 
 where t2.v2 IS null

 UNION ALL
 select 
   path.start ,
   t1.v2 as end,
   path.path || '>' || t1.v1,       
   path.d + 1 
 from path 
   inner join topo as t1 on t1.v1=path.end
)
SELECT * FROM path

只需添加几个字段即可跟踪遍历层次结构时发生的情况。 Start 将从第一个查询开始是静态的。每条记录都将是 1，因为这是您的起点。 End 是您当前正在工作的任何节点。 path 将在找到每个新节点时连接结束节点。 depth 会告诉你你走过了多远。

将一个递归查询的输出重定向到另一个递归查询

Redirect output of one recursive query into another recursive query

sql

postgresql

recursive-query

topological-sort