Question

我有一个递归查询

With RECURSIVE tree AS
 (
 SELECT * FROM comments WHERE id = 83
 UNION
 SELECT t.*
      From comments t
 JOIN tree rt ON rt.parent_id = t.id

 )
 SELECT * from tree ORDER BY id DESC LIMIT 5

我将如何通过ASC再订购一次？

Edit1 ：尝试了以下解决方案： Get the last N rows in the database in order?

With RECURSIVE tree AS
 (
 SELECT * FROM comments WHERE id = 83
 UNION
 SELECT t.*
      From comments t
 JOIN tree rt ON rt.parent_id = t.id

 )
 select * from (SELECT * from tree ORDER BY id DESC LIMIT 5) order by id

给我一个错误：

ERROR:  subquery in FROM must have an alias

Answer 1

select * from (SELECT * from tree ORDER BY comment_id DESC LIMIT 5) t order by comment_id

Answer 2

在PostgreSQL中，所有表表达式（FROM之后的选择）都需要命名。也就是说，他们需要有一个别名。只需添加任何别名即可。例如，我添加了x，如下所示：

With RECURSIVE tree AS
 (
 SELECT * FROM comments WHERE id = 83
 UNION
 SELECT t.*
      From comments t
 JOIN tree rt ON rt.parent_id = t.id

 )
 select * from (SELECT * from tree ORDER BY id DESC LIMIT 5) x order by id

您发现了吗？

Postgres ORDER BY两次DESC然后是ASC

2 个答案: