Question

我的第一个查询返回前10条注释，其parent_id为空

SELECT comment_id FROM comments WHERE thread_id = $1
AND parent_id is NULL 
ORDER BY upvoted DESC FETCH FIRST 10 ROW ONLY

我将如何使用每个注释ID来执行递归查询？

我当前的方法是将返回的comment_id存储在数组中

[1, 2, 3, 4, 10, 14, 15, 18, 19, 20]

，然后使用for循环对每个id进行递归查询

var query = 

 `With RECURSIVE cte AS
 (
   SELECT * FROM comments WHERE comment_id = $1
   UNION
   SELECT t.*
   From comments t
   JOIN cte rt ON rt.comment_id = t.parent_id
 )
 SELECT * FROM cte`;


for(int i = 0; i < array.size(); i++){

   client.query(query, array[i])
   . . .
}

所以我想知道如何在单个查询中做到这一点，而不是将ID存储在数组中，然后递归查询每个ID？

Answer 1

您可以将第一个语句用作递归查询的非递归部分。但是由于需要的顺序，您需要将该查询放在括号之间：

With RECURSIVE cte AS
(
   (
    SELECT * 
    FROM comments 
    WHERE thread_id = $1
      AND parent_id is NULL 
    ORDER BY upvoted DESC 
    FETCH FIRST 10 ROW ONLY
   )
   UNION
   SELECT t.*
   From comments t
     JOIN cte rt ON rt.comment_id = t.parent_id
 )
 SELECT * FROM cte`

或者，您也可以在单独的CTE中进行此操作：

With RECURSIVE root_nodes AS
(
    SELECT * 
    FROM comments 
    WHERE thread_id = $1
      AND parent_id is NULL 
    ORDER BY upvoted DESC 
    FETCH FIRST 10 ROW ONLY
), cte as (
   select * 
   from root_nodes

   UNION

   SELECT t.*
   From comments t
     JOIN cte rt ON rt.comment_id = t.parent_id
)
SELECT * 
FROM cte;

请注意，即使第一个CTE不是递归关键字，recursive关键字也属于WITH。

PostgreSQL：结合这两个查询

1 个答案: