在 BigQuery 表中展平多个相同大小的数组列

Question

我有一个包含几列的表，其中一些列是相同长度的 arrays。 我想取消嵌套它们以获得来自 arrays 的值在单独的行中的结果。

所以有这样的表：

我想去：

这是其中一个数组列的工作方式：

WITH data AS
(
  SELECT 1001 as id, ['a', 'b', 'c'] as array_1, [1, 2, 3] as array_2
  UNION ALL
  SELECT 1002 as id, ['d', 'e', 'f', 'g'] as array_1, [4, 5, 6, 7] as array_2
  UNION ALL
  SELECT 1003 as id, ['h', 'i'] as array_1, [8, 9] as array_2
)
SELECT id, a1
FROM data,
UNNEST(array_1) as a1

有没有一些优雅的方法可以同时取消两个 arrays ？ 我想避免单独取消嵌套每一列，然后将所有内容连接在一起。

Answer 1

以下是 BigQuery 标准 SQL

#standardSQL
SELECT id, a1, a2
FROM data, UNNEST(array_1) AS a1 WITH OFFSET 
JOIN UNNEST(array_2) AS a2 WITH OFFSET
USING(OFFSET)

Answer 2

您可以使用with offset和join ：

WITH data AS
(
  SELECT 1001 as id, ['a', 'b', 'c'] as array_1, [1, 2, 3] as array_2
  UNION ALL
  SELECT 1002 as id, ['d', 'e', 'f', 'g'] as array_1, [4, 5, 6, 7] as array_2
  UNION ALL
  SELECT 1003 as id, ['h', 'i'] as array_1, [8, 9] as array_2
)
SELECT id, a1, a2
FROM data cross join
     UNNEST(array_1) as a1 with offset n1 JOIN
     UNNEST(array_2) as a2 with offset n2 
     on n1 = n2

Answer 3

因此，我自己对 SQL 中的取消嵌套进行了一些研究，并提出了以下解决方案：

WITH data AS
(
  SELECT 1001 as id, ['a', 'b', 'c'] as array_1, [1, 2, 3] as array_2
  UNION ALL
  SELECT 1002 as id, ['d', 'e', 'f', 'g'] as array_1, [4, 5, 6, 7] as array_2
  UNION ALL
  SELECT 1003 as id, ['h', 'i'] as array_1, [8, 9] as array_2
)
SELECT id, a1, array_2[OFFSET(off)] AS a2
FROM data
CROSS JOIN UNNEST(array_1) AS a1 WITH OFFSET off

优点是它不需要取消嵌套所有 arrays，只需一个。