Question

假设我有一个包含以下架构的表

name       | type
----------------------
id         | STRING
timestamp  | TIMESTAMP
event_type | STRING
some_value | STRING
...

我希望获得'x'类型的所有事件。但是，我还想为返回的每一行添加一个附加参数。如果最近的事件TRUE具有WHERE event_type='y'，则此参数为布尔值some_value='necessary value'。

例如，假设以下行按时间戳递增排序：

event_type |  some_value
------------------------
y          | 'true value'
x          | 'not relevant'
y          | 'false value'
x          | 'not relevant 2'
y          | 'true value'
y          | 'false value'
x          | 'not relevant3'
x          | 'not relevant4'

我会从查询中获得以下行：

event_type |  some_value     | previous_true
-------------------------------------
x          | 'not relevant'  | TRUE
x          | 'not relevant2' | FALSE
x          | 'not relevant3' | FALSE
x          | 'not relevant4' | FALSE

我认为加入可能会成功，但我无法弄清楚它是如何起作用的。 LAG一开始似乎也是一个好主意，但后来我意识到LAG将采用前一行而不管它是什么，我不确定如何使用它。

Answer 1

使用BigQuery Standard SQL - 请尝试以下
（确保取消选中显示选项 下的Use Legacy SQL复选框）

WITH YourTable AS (
  SELECT 1 AS ts, 'y' AS event_type, 'true value' AS some_value UNION ALL
  SELECT 2 AS ts, 'x' AS event_type, 'not relevant' AS some_value UNION ALL
  SELECT 3 AS ts, 'y' AS event_type, 'false value' AS some_value UNION ALL
  SELECT 4 AS ts, 'x' AS event_type, 'not relevant2' AS some_value UNION ALL
  SELECT 5 AS ts, 'y' AS event_type, 'true value' AS some_value UNION ALL
  SELECT 6 AS ts, 'y' AS event_type, 'false value' AS some_value UNION ALL
  SELECT 7 AS ts, 'x' AS event_type, 'not relevant3' AS some_value UNION ALL
  SELECT 8 AS ts, 'x' AS event_type, 'not relevant4' AS some_value
)
SELECT 
  event_type, 
  some_value,
  (SELECT some_value = 'true value' FROM YourTable 
    WHERE event_type = 'y' AND ts < a.ts
    ORDER BY ts DESC LIMIT 1
    ) AS previous_true
FROM YourTable AS a
WHERE event_type = 'x'
ORDER BY ts

结果是：

event_type  some_value      previous_true    
x           not relevant    true     
x           not relevant2   false    
x           not relevant3   false    
x           not relevant4   false

对于BigQuery Legacy SQL - 尝试

SELECT
  event_type, some_value, 
  previous_true = 'true value' AS previous_true
FROM (
  SELECT
    ts, event_type, some_value, 
    FIRST_VALUE(some_value) OVER(PARTITION BY grp ORDER BY ts) AS previous_true
  FROM (
    SELECT 
      ts, event_type, some_value, 
      SUM(step) OVER(ORDER BY ts) AS grp
    FROM (
      SELECT 
        ts, event_type, some_value, 
        IF(event_type = 'x' , 0, 1) AS step
      FROM 
        (SELECT 1 AS ts, 'y' AS event_type, 'true value' AS some_value),
        (SELECT 2 AS ts, 'x' AS event_type, 'not relevant' AS some_value),
        (SELECT 3 AS ts, 'y' AS event_type, 'false value' AS some_value),
        (SELECT 4 AS ts, 'x' AS event_type, 'not relevant2' AS some_value),
        (SELECT 5 AS ts, 'y' AS event_type, 'true value' AS some_value),
        (SELECT 6 AS ts, 'y' AS event_type, 'false value' AS some_value),
        (SELECT 7 AS ts, 'x' AS event_type, 'not relevant3' AS some_value),
        (SELECT 8 AS ts, 'x' AS event_type, 'not relevant4' AS some_value)
    )
  )
)
WHERE event_type = 'x'
ORDER BY ts

Answer 2

以下是一种方法：您可以使用＆＃34; y＆＃34;得到每个＆＃34; x＆＃34;的最近y的id。然后使用join进行计算：

select t.*,
       (case when some_value = 'necessary value' then 1 else 0 end) as previous_true
from (select t.*,
             max(case when event_type = 'y' then id end) over (order by timestamp) as yid
      from t
     ) t join
     t ty
     on ty.id = t.yid
where t.event_type = 'x';

我不确定id和timestamp的确切角色。此版本假定id相对于timestamp统一增加。或者，您可以使用timestamp - 但不清楚这对join是否足够。

BigQuery：获取有关最近的前一行的行+信息，其中列x在前一行中具有某些值

2 个答案: