在bigquery

Question

我有以下代码段

WITH sequences AS
  (SELECT 1 AS id, [STRUCT(0 AS a, 1 AS b)] AS some_numbers
   UNION ALL SELECT 2 AS id, [STRUCT(2 AS b, 4 AS a)] AS some_numbers
   UNION ALL SELECT 3 AS id, [STRUCT(5 AS b, 3 AS a), STRUCT (7 AS b, 4 AS a)]
     AS some_numbers)
SELECT id AS matching_rows
FROM sequences
WHERE EXISTS (SELECT 1
              FROM UNNEST(some_numbers)
              WHERE b > 3);

我得到以下输出

Row	matching_rows	
1	    2
2       3

根据where条件，结果必须仅是第三行。为什么还要显示第二行？？

Answer 1

结构字段是按位置而非名称进行合并的。所以这个：

WITH sequences AS
  (SELECT 1 AS id, [STRUCT(0 AS a, 1 AS b)] AS some_numbers
   UNION ALL SELECT 2 AS id, [STRUCT(2 AS b, 4 AS a)] AS some_numbers
   UNION ALL SELECT 3 AS id, [STRUCT(5 AS b, 3 AS a), STRUCT (7 AS b, 4 AS a)]
     AS some_numbers)
SELECT id AS matching_rows
FROM sequences
WHERE EXISTS (SELECT 1
              FROM UNNEST(some_numbers)
              WHERE b > 3);

等效于此：

WITH sequences AS
  (SELECT 1 AS id, [STRUCT(0 AS a, 1 AS b)] AS some_numbers
   UNION ALL SELECT 2 AS id, [STRUCT(2 AS a, 4 AS b)] AS some_numbers
   UNION ALL SELECT 3 AS id, [STRUCT(5 AS a, 3 AS b), STRUCT (7 AS a, 4 AS b)]
     AS some_numbers)
SELECT id AS matching_rows
FROM sequences
WHERE EXISTS (SELECT 1
              FROM UNNEST(some_numbers)
              WHERE b > 3);

除了联合中的第一个查询外，您还可以删除AS <name>别名，因为它们不会影响结果。