Google BigQuery，當使用'unnest'功能時，我丟失了空行

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 

當我執行此代碼時，我預計結果如下。

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 

但我下的結果得到...

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。 然後，我看到谷歌的官方文件。有這樣寫的。

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

但我不想丟失我的空行。

如何保持空行？

請告訴我的解決方案...

Answer 1

相反的CROSS JOIN，使用LEFT JOIN。這將返回一個空數組爲空的行。您也可能對文檔中的working with arrays topic感興趣。

#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;