sql - Google BigQuery，使用 'unnest' 函数时丢失了空行

Question

#StandardSQL
WITH tableA AS (
SELECT ["T001", "T002", "T003"] AS T_id, [1, 5] AS L_id
UNION ALL
SELECT ["T008", "T009"] AS T_id, NULL AS L_id
)

SELECT * FROM tableA, UNNEST(L_id) AS unnest

当我执行这段代码时，我期望得到如下结果。

RowNumber  T-id            L-id  unnest
1          T001,T002,T003  1,5   1
2          T001,T002,T003  1,5   5
3          T004,T005       NULL  NULL

但我得到了这个结果:

RowNumber  T-id            L-id  unnest
1          T001,T002,T003  1,5   1
2          T001,T002,T003  1,5   5

我失去了第三排。然后，我看到Google官方文档，里面是这么说的:

UNNEST treats NULL as follows.
 ・NULL and empty ARRAY generate zero rows.
 ・An ARRAY containing NULL generates a row containing a NULL value.

但我不想丢失空行。

如何保留空行？

请告诉我解决方案...

Answer 1

使用 LEFT JOIN 代替 CROSS JOIN。这将为空数组返回一个包含 null 的行。您可能还对 working with arrays topic 感兴趣来自文档。

#StandardSQL
WITH tableA AS (
  SELECT ["T001", "T002", "T003"] AS T_id, [1, 5] AS L_id
  UNION ALL
  SELECT ["T008", "T009"] AS T_id, NULL AS L_id
)
SELECT * FROM tableA
LEFT JOIN UNNEST(L_id) AS value;