添加缺少的日期行继承以前的值

Question

我正在尝试使用 Big Query 获取“期望结果”上的 table（见下图），从一个 Dummy table 开始，它可以按如下方式初始化：

with dummy_data as
(
  select * from unnest([
    struct(
      date('2021-06-10') AS timestamp,
      'A' AS category,
      '5' as value),
    (date('2021-06-11'), 'B', '3'),
    (date('2021-06-12'), 'C', '2'),
    (date('2021-06-14'), 'A', '7')
  ])
)
select * from dummy_data

我从生成时间序列和交叉连接开始，但无法摆脱由此产生的不必要的行：

with dummy_data as
(
  select * from unnest([
    struct(
      date('2021-06-10') AS timestamp,
      'A' AS category,
      '5' as values ),
    (date('2021-06-11'), 'B', '3'),
    (date('2021-06-12'), 'C', '2'),
    (date('2021-06-14'), 'A', '7')
  ])
),
-- Initialize date series that covers needed range
date_series as (
    select
        *
    from 
        unnest(generate_date_array('2021-06-10', '2021-06-14', interval 1 day)) as date
),
-- cross_join
cross_join as (
    select * from dummy_data
    cross join date_series
)
select * from cross_join

结果如下（蓝色行是我需要的新行，灰色行是我想删除的行）：

谢谢！

Answer 1

考虑以下方法

select  timestamp, category, value 
from (
  select timestamp as start_timestamp, category, value, ifnull(
    lead(timestamp) over(partition by category order by timestamp) - 1,
    max(timestamp) over(order by timestamp desc) 
    ) next_timestamp
  from dummy_data
), unnest(generate_date_array(start_timestamp, next_timestamp)) timestamp

如果应用于您问题中的示例数据 - 输出为

添加缺少的日期行继承以前的值

Add missing date rows inheriting the previous value

sql

google-bigquery