将 bigquery 中的数组与空数组连接起来

Question

我有一个 table 看起来像这样：

然后我尝试将每种标签的label1、label2、label3聚合到一个数组中，然后，最后我想将所有非空标签放入一个组合数组中。所以我的查询看起来像这样

#standardSQL
WITH
table AS (
SELECT 'abc' id, 1 label1, 12 label2, 122 label3 UNION ALL
SELECT 'abc', 1, 12, 129 UNION ALL
SELECT 'xyz', 2, 23, NULL UNION ALL
SELECT 'xyz', 2, 24, NULL
),

each_label_agg AS (
 SELECT
 id,
 ARRAY_AGG(label1 IGNORE NULLS) AS label1_agg,
 ARRAY_AGG(label2 IGNORE NULLS) AS label2_agg,
 ARRAY_AGG(label3 IGNORE NULLS) AS label3_agg
FROM
table
GROUP BY
 id)
SELECT
 each_label_agg.*,
 ARRAY_CONCAT(each_label_agg.label1_agg, each_label_agg.label2_agg, 
 each_label_agg.label3_agg) AS combined_labels
FROM
 each_label_agg

输出如下所示：

但是在输出中我期望 combined_labels 是 [2,2,23,24] for id xyz.

ignore nulls 参数在 array_concat 中不起作用。我猜测 combined_labels 由于 label3 处的空数组而变得畸形。如何获得 xyz 的预期 combined_labels 为 [2,2,23,24]？

Answer 1

#standardSQL
WITH table AS (
  SELECT 'abc' id, 1 label1, 12 label2, 122 label3 UNION ALL
  SELECT 'abc', 1, 12, 129 UNION ALL
  SELECT 'xyz', 2, 23, NULL UNION ALL
  SELECT 'xyz', 2, 24, NULL
), each_label_agg AS (
 SELECT
   id,
   ARRAY_AGG(label1 IGNORE NULLS) AS label1_agg,
   ARRAY_AGG(label2 IGNORE NULLS) AS label2_agg,
   ARRAY_AGG(label3 IGNORE NULLS) AS label3_agg
  FROM table
  GROUP BY id
)
SELECT
  each_label_agg.*,
  ARRAY_CONCAT(
   IFNULL(each_label_agg.label1_agg, []), 
   IFNULL(each_label_agg.label2_agg, []),
   IFNULL(each_label_agg.label3_agg, [])
  ) AS combined_labels
FROM each_label_agg

Answer 2

造成此问题的原因是 BigQuery 有 limitations respect to NULL values and the array generation will return NULL if any argument is NULL as documented here。因此，用它们代替空数组很方便（因为 NULLs 和空数组在 BigQuery 中是两个不同的值）

将 bigquery 中的数组与空数组连接起来

Concatenating arrays in bigquery with empty arrays

google-bigquery

bigquery-standard-sql