在 BQ 中嵌套 table 时如何避免数组 uf NULLS

Question

我正在加入 2 tables，连接在左边，第二个 table 没有第一个的所有键，所以它在右边产生 NULL。将其分组到数组中时如何避免它们？

例如：

with 
  t1 AS (select 1 AS c1, 2 AS c2 UNION ALL select 5, 6),
  t2 AS (select 3 AS c1, 4 AS c4 UNION ALL select 3, 5, UNION ALL select 3,4, UNION ALL select 5,6)
SELECT t2.c1, ARRAY_AGG(DISTINCT t2.c4), ARRAY_AGG((SELECT AS STRUCT t1.*))
FROM t2 LEFT JOIN t1 ON t1.c1=t2.c1
GROUP BY t2.c1

结果是：

我期望的是第一行第二行只有一行 NULL table，类似（抱歉画得不好）：

Answer 1

是否可以删除所有空语句？

然后在 array_agg

中使用 if 语句

with 
  t1 AS (select 1 AS c1, 2 AS c2 UNION ALL select 5, 6),
  t2 AS (select 3 AS c1, 4 AS c4 UNION ALL select 3, 5, UNION ALL select 3,4, UNION ALL select 5,6)
SELECT t2.c1, ARRAY_AGG(DISTINCT t2.c4), ARRAY_AGG( if(t1.c1 is null   , null, STRUCT(t1) ) ignore nulls  ), 
FROM t2 LEFT JOIN 
t1 
 ON t1.c1=t2.c1

GROUP BY t2.c1

在 BQ 中嵌套 table 时如何避免数组 uf NULLS

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