Google bigquery 在大查询中使用'Lead'窗口函数时出现时间戳问题

我正在尝试获取客户的第一个订单，他们的下一个订单，以及两个订单之间的天数差。看起来很简单。我采取的步骤如下：

使用MIN（）和LEAD（）函数提取客户的第一个和第二个订单

使用这两个字段运行DATEDIFF以获得天数差异

简短代码如下所示：

SELECT cust, MIN(ord_time) first_ord, LEAD(ord_time, 1) 
                                      OVER 
                                      (PARTITION BY customer_id
                                      ORDER BY ord_time) next_ord
FROM
(SELECT cust, ord_time
FROM df.orders
GROUP EACH BY cust, ord_time)

这里还有其他一些过滤连接和分组，但这是基本块

输出应该是一个带有客户ID的字段和两个时间戳字段。两个时间戳字段如下所示：

所以一切看起来都很好。但是，当我尝试使用这两个字段运行DATEDIFF（）函数时，所有内容都返回Null

此外，当我将鼠标悬停在任一时间戳字段上时，它会告诉我数据类型是时间戳，但当我尝试运行任何类型的时间戳转换到秒或任何其他值时，下一个ord字段会导致它失败，并出现“类型未知”错误

我只是在寻找我做错了什么，或者有没有办法解决这个问题

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谢谢你的帮助。

我认为这与wondow函数如何处理时间戳有关

这就是我目前看到的情况：

1. 当源数据点为字符串时，所有数据点均按预期工作：

SELECT 
  customer_id,
  first_ord,
  next_ord,
  DATEDIFF(next_ord, first_ord) AS diff
FROM (
  SELECT 
    customer_id, 
    LEAD(ord_time, 0) OVER (PARTITION BY customer_id ORDER BY ord_time) first_ord, 
    LEAD(ord_time, 1) OVER (PARTITION BY customer_id ORDER BY ord_time) next_ord,
    ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY ord_time) num
  FROM 
    (SELECT 1 AS customer_id, '2014-04-08 09:51:24 UTC' AS ord_time),
    (SELECT 1 AS customer_id, '2014-04-08 09:53:31 UTC' AS ord_time),
    (SELECT 1 AS customer_id, '2014-05-08 09:53:31 UTC' AS ord_time),
    (SELECT 2 AS customer_id, '2014-09-12 17:20:43 UTC' AS ord_time),
    (SELECT 2 AS customer_id, '2015-04-16 21:44:18 UTC' AS ord_time),
)
WHERE num = 1

结果：

customer_id       first_ord             next_ord    diff     
1   2014-04-08 09:51:24 UTC 2014-04-08 09:53:31 UTC 0    
2   2014-09-12 17:20:43 UTC 2015-04-16 21:44:18 UTC 216  

2. 当源数据点为时间戳时-结果为null，如您在问题中所述：

SELECT 
  customer_id,
  first_ord,
  next_ord,
  DATEDIFF(next_ord, first_ord) AS diff
FROM (
  SELECT 
    customer_id, 
    LEAD(ord_time, 0) OVER (PARTITION BY customer_id ORDER BY ord_time) first_ord, 
    LEAD(ord_time, 1) OVER (PARTITION BY customer_id ORDER BY ord_time) next_ord,
    ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY ord_time) num
  FROM 
    (SELECT 1 AS customer_id, TIMESTAMP('2014-04-08 09:51:24 UTC') AS ord_time),
    (SELECT 1 AS customer_id, TIMESTAMP('2014-04-08 09:53:31 UTC') AS ord_time),
    (SELECT 1 AS customer_id, TIMESTAMP('2014-05-08 09:53:31 UTC') AS ord_time),
    (SELECT 2 AS customer_id, TIMESTAMP('2014-09-12 17:20:43 UTC') AS ord_time),
    (SELECT 2 AS customer_id, TIMESTAMP('2015-04-16 21:44:18 UTC') AS ord_time),
)
WHERE num = 1

结果:

customer_id       first_ord             next_ord    diff     
1   2014-04-08 09:51:24 UTC 2014-04-08 09:53:31 UTC 0    
2   2014-09-12 17:20:43 UTC 2015-04-16 21:44:18 UTC 216  

customer_id       first_ord             next_ord    diff     
1   2014-04-08 09:51:24 UTC 2014-04-08 09:53:31 UTC null     
2   2014-09-12 17:20:43 UTC 2015-04-16 21:44:18 UTC null     

3. 为了“修复”，我必须进行如下铸造：

SELECT 
  customer_id,
  TIMESTAMP(first_ord) as first_ord,
  TIMESTAMP(next_ord) as next_ord,
  DATEDIFF(next_ord, first_ord) AS diff
FROM (
  SELECT 
    customer_id, 
    LEAD(STRING(ord_time), 0) OVER (PARTITION BY customer_id ORDER BY ord_time) first_ord, 
    LEAD(STRING(ord_time), 1) OVER (PARTITION BY customer_id ORDER BY ord_time) next_ord,
    ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY ord_time) num
  FROM 
    (SELECT 1 AS customer_id, TIMESTAMP('2014-04-08 09:51:24 UTC') AS ord_time),
    (SELECT 1 AS customer_id, TIMESTAMP('2014-04-08 09:53:31 UTC') AS ord_time),
    (SELECT 1 AS customer_id, TIMESTAMP('2014-05-08 09:53:31 UTC') AS ord_time),
    (SELECT 2 AS customer_id, TIMESTAMP('2014-09-12 17:20:43 UTC') AS ord_time),
    (SELECT 2 AS customer_id, TIMESTAMP('2015-04-16 21:44:18 UTC') AS ord_time)
)
WHERE num = 1

结果是：

customer_id       first_ord             next_ord    diff     
1   2014-04-08 09:51:24 UTC 2014-04-08 09:53:31 UTC 0    
2   2014-09-12 17:20:43 UTC 2015-04-16 21:44:18 UTC 216  

---

这太棒了。我没想到要在窗口功能内进行任何铸造。我所有的尝试都是在完成计算之后进行的。