如何添加一个列，该列根据另一列的条件对其他列的值进行字符串加法

Question

我有一张这样的桌子：

column1       column2
product1    action_of_interest1
product2    action_of_interest1
product3    random_action
product1    action_of_interest2

我想添加一个new_column （一个用逗号分隔的条目），它在 column2 值为 action_of_interest1 时添加/连接来自 column1 的条目，并在 column2 值为 ` action_of_interest1时减去运行的连接数组。 对于 random_actions，什么也不做，只打印当前数组。

这是结果表：

column 1          column2                         new_column
product1     action_of_interest1                   product1
product2     action_of_interest1                  product1,product2
product3     random_action                    product1,product2
product1     action_of_interest2                  product2

如何在 BigQuery/SQL 中执行此操作？

Answer 1

使用 window 函数的方法：

WITH sample AS (
  SELECT "product1" AS column1, "action_of_interest1" AS column2, 1 AS column3
  UNION ALL
  SELECT "product2" AS column1, "action_of_interest1" AS column2, 2 AS column3
  UNION ALL
  SELECT "product3" AS column1, "random_action" AS column2, 3 AS column3
  UNION ALL
  SELECT "product1" AS column1, "action_of_interest2" AS column2, 4 AS column3
),
running_agg as (
  SELECT
    *,
    ARRAY_AGG(IF(column2 = 'action_of_interest1', column1, '')) OVER (ORDER BY column3 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as action_of_interest1,
    ARRAY_AGG(IF(column2 = 'action_of_interest2', column1, '')) OVER (ORDER BY column3 ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as action_of_interest2
  FROM sample
)
SELECT 
  * EXCEPT (action_of_interest1, action_of_interest2),
  ARRAY_TO_STRING(
    ARRAY(
      SELECT * FROM UNNEST(action_of_interest1) 
      EXCEPT DISTINCT 
      SELECT * FROM UNNEST(action_of_interest2)
    ), 
    ','
  ) AS new_column
FROM running_agg

Output：

column1     column2                 column3     new_column
product1    action_of_interest1     1           product1
product2    action_of_interest1     2           product1,product2
product3    random_action           3           product1,product2
product1    action_of_interest2     4           product2