Question

我有一个在标准sql上运行良好的查询，但redshift有一些限制，不允许在内部select中引用外部查询信息的查询。

查询的基本思想是从上次客户发布响应时生成时间戳的差异。我有一个论坛的客户发布时间戳，我想知道他们发布的时间，自上次发布以来时间差异是什么。这是在sql中运行测试数据的查询，具有预期输出：http://sqlfiddle.com/#!9/04358/2

以下是查询：

SELECT
  current.id,
  current.datetime,
  TIMESTAMPDIFF(minute, current.datetime, IFNULL(next.datetime, 
current.datetime)) as diff
FROM
  TestTable as current
LEFT JOIN
  TestTable as next
    on next.datetime = (select min(datetime) from TestTable
      where datetime > current.datetime and id = current.id)
order by
  current.id, current.datetime

在redshift中，由于不支持子查询模式，因此不起作用。有任何想法如何将其变成非参考子查询？

Answer 1

您不需要派生表。使用窗口函数first_value来获取id最后一次发布评论并将其用于减法。

SELECT
id,
datetime,
DATEDIFF(minute, datetime, first_value(datetime) over(partition by id order by datetime desc rows between unbounded preceding and unbounded following)) as diff
FROM TestTable

我不确定Redshift中的另一个函数内是否有窗函数。在那种情况下试试，

SELECT
id,
datetime,
DATEDIFF(minute, datetime, last_response_time) as diff
FROM (SELECT t.*,first_value(datetime) over(partition by id order by datetime desc rows between unbounded preceding and unbounded following) as last_response_time
      FROM TestTable t
     ) t

redshift子查询引用问题 - 自连接和分钟

1 个答案: