如何在连接两个表时获取所需日期值为NULL的下一个可用日期值

Question

在BigQuery中联接两个表时出现问题。请参阅所附图片。表1列出了公司备案的截止日期，表2列出了历史股价。过去五年中大多数公司的截止日期是相同的，一年（30/09/2018）是一个周末，因此该日没有股价。因此，如何在联接Table1.date = Table2.date的两个表时从Table2的下一个可用日期获取值。谁能让我知道如何在BigQuery中执行查询？

谢谢， 湿婆神

Answer 1

在注释部分中澄清后，我能够使用StandardSQL创建查询以实现您的目标。

我使用了内置函数LEAD()，该函数根据分区和/或顺序返回下一行的值。下面是查询：

WITH table1 AS (
SELECT DATE(2015,09,30) as end_date, 20 as share_price UNION ALL
SELECT DATE(2016,09,30) as end_date, 30 as share_price UNION ALL
SELECT DATE(2017,09,30) as end_date, 40 as share_price UNION ALL
SELECT DATE(2018,09,30) as end_date, NULL as share_price UNION ALL
SELECT DATE(2019,09,30) as end_date, 60 as share_price 
), 
table2 AS(
SELECT DATE(2015,09,30) as date, 20 as share_price UNION ALL
SELECT DATE(2016,09,30) as date, 30 as share_price UNION ALL
SELECT DATE(2017,09,30) as date, 40 as share_price UNION ALL
SELECT DATE(2018,09,30) as date, NULL as share_price UNION ALL
SELECT DATE(2018,10,01) as date, 50 as share_price UNION ALL
SELECT DATE(2019,09,30) as date, 60 as share_price 
),
table2_ref AS (
SELECT date, 
IF(share_price IS NULL, LEAD(share_price,1) OVER (ORDER BY date), share_price) AS share_price 

#this following column is not necessary, it is just to check which null values were modified
,IF(share_price IS NULL, "got the next available value", "kept the value") AS check

FROM table2
ORDER BY date
)
SELECT a.date, a.share_price FROM table2_ref a INNER JOIN table1 b ON a.date = b.end_date

输出，

请注意，我已在 table2_ref 中使用了 check 列，以便跟踪更改了哪些值从空到下一个可用价格。因此，它只是可以在输出中检查的标志，但是您可以在代码中取消显示此列（就像我在上面的输出图像中所做的一样）。