SQL 子查询问题，“错误:对 FROM 子句条目的无效引用..." [英] SQL subquery questions, "ERROR: invalid reference to FROM-clause entry ..."

问题描述

SQL 遇到问题(目前使用 postgresql)

Having trouble with SQL (currently using postgresql)

我有这个查询，因为我需要比较最近的项目和第二个最近的项目:

I have this query as I need to compare the most recent item and the second most recent item:

SELECT p1.*, p2.price_cents FROM "prices" p1 
  INNER JOIN 
    (
      SELECT price_cents, game_id from prices as p WHERE p.game_id = p1.game_id 
        ORDER BY p.created_at DESC LIMIT 1 OFFSET 1
    )
  p2 ON p2.game_id = p1.game_id 

这会产生一些错误:

ERROR:  invalid reference to FROM-clause entry for table "p1"
LINE 1: ...AND p.game_id = p1.game_id...
                           ^
HINT:  There is an entry for table "p1", but it cannot be referenced from this part of the query.

是否有任何原因我无法从该子选择访问 p1，是否存在问题，例如 p1 的数据尚不可用?有没有另一种方法可以通过 JOIN 做到这一点?

Is there any reason I can't access p1 from that subselect, is it a existence issue, as in, p1's data isn't available yet? Is there another way to do this with a JOIN?

推荐答案

试试这个

SELECT p1.*, (
    SELECT price_cents 
    FROM "prices" p 
    WHERE p1.game_id = p.game_id  
    ORDER BY p.created_at DESC LIMIT 1 OFFSET 1
) as price_cents 
FROM "prices" p1 

更新根据作者评论

如果您需要第二个最近条目中的多列，您可以尝试以下代码段

If you need more than one column from second recent entry, you can try following snippet

SELECT * FROM (
    SELECT p.*, (
        SELECT id 
        FROM "prices" 
        WHERE p.game_id = game_id  
        ORDER BY created_at DESC LIMIT 1 OFFSET 1
    ) AS second_id 
    FROM "prices" p
) p1 INNER JOIN "prices" p2 ON p1.second_id = p2.id

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