BigQuery 物化视图 - 组中最后一个

Question

在 BigQuery 中，是否可以创建一个物化视图，其中包含基表中每个组的最新行。

例如

CREATE TABLE basetable (
  group_id INT64, timestamp TIMESTAMP, value FLOAT64
);

INSERT INTO basetable (group_id, timestamp, value) VALUES
(1, '2020-01-01', 0.1), 
(1, '2020-01-02', 0.2),
(2, '2020-01-02', 0.1),
(2, '2020-01-01', 0.2);

Base table
+----------+--------------+-------+
| group_id | timestamp    | value |
+----------+--------------+-------+
|    1     | '2020-01-01' |   0.1 |
|    1     | '2020-01-02' |   0.2 |
|    2     | '2020-01-02' |   0.1 |
|    2     | '2020-01-01  |   0.2 |
+----------+--------------+-------+

我希望物化视图如下所示

Materialized view 
+----------+--------------+-------+
| group_id | timestamp    | value |
+----------+--------------+-------+
|    1     | '2020-01-02' |   0.2 |
|    2     | '2020-01-02' |   0.1 |
+----------+--------------+-------+

BigQuery 物化视图不支持分析函数或联接。还有其他方法可以创建这样的视图吗？

Answer 1

您最多可以这样做，请注意结果是一个包含一项的数组

CREATE MATERIALIZED VIEW  name as
SELECT group_id,
max(t.timestamp) as timestamp,
ARRAY_AGG(t.value  IGNORE NULLS ORDER BY t.timestamp DESC LIMIT 1) as value 
FROM table t
group by group_id

那么你还需要一个视图

create view viewname as
SELECT group_id,timestamp
cast(value [safe_offset(0)] as string) as  value 
FROM materialized_view