就顾虑而言，Big Query在窗口函数中不支持ignore null。这是一个依赖于窗口最大值的解决方案，用于查找保存最后一个非空owner_id的记录（假定时间戳的唯一性）。掌握了这些信息之后，您就可以通过联接引入相应的owner_id。

select 
    c.timestamp,coalesce(c.owner_id,c_lag.owner_id) owner_id,c.owner_assigneddate,c.lastmodifieddate
from 
    (
        select
            cte.*,max(case when owner_id is not null then timestamp end) 
                over(order by timestamp rows unbounded preceding) target_timestamp
        from cte
    ) c
    left join cte c_lag 
        on c.owner_id is null 
        and c_lag.timestamp = c.target_timestamp

Demo on DB Fiddle ：

timestamp           | owner_id | owner_assigneddate  | lastmodifieddate    
:------------------ | -------: | :------------------ | :-------------------
2019-11-12 16:01:55 |     null | null                | null                
2019-11-12 19:03:18 | 39530934 | 2019-11-12 19:03:18 | 2019-11-12 19:03:18 
2019-11-12 19:03:19 | 39530934 | null                | 2019-11-12 19:03:19 
2019-11-12 19:03:20 | 39530934 | null                | 2019-11-12 19:03:20 
2019-11-12 19:03:31 | 40320368 | 2019-11-12 19:03:31 | 2019-11-12 19:03:31 
2019-11-12 19:03:33 | 40320368 | null                | 2019-11-12 19:03:33 
2019-11-12 19:03:56 | 40320368 | null                | 2019-11-12 19:03:356

注意：为了更好地理解逻辑（如果需要），您可以独立运行内部查询以查看其返回的内容（请参阅数据库提琴）。

修改

重新阅读此内容，我发现window max所提供的信息已经在您的原始数据中的owner_assigneddate列中了......这样简单得多：

select 
    c.timestamp,c.lastmodifieddate
from
    cte c
    left join cte c_lag 
        on c.owner_id is null 
        and c_lag.timestamp = c.owner_assigneddate

这应符合您的cte定义：

...
select timestamp,owner_id,owner_assigneddate,lastmodifieddate,LAST_VALUE(owner_id IGNORE NULLS) 
            OVER(ORDER BY timestamp ASC ROWS BETWEEN 
                 UNBOUNDED PRECEDING AND CURRENT ROW) AS test_column
from cte order by timestamp asc 

在BigQuery中，将LAST_VALUE()与IGNORE NULLS选项和 COALESCE()一起使用：

select timestamp,COALESCE(owner_id,last_value(owner_id ignore nulls) over (order by timestamp)) as owner_id,COALESCE(owner_assigneddate,LAST_VALUE(owner_assigneddate IGNORE NULLS) OVER (ORDER BY TIMESTAMP)) as owner_assigneddate,COALESCE(lastmodifieddate,LAST_VALUE(lastmodifieddate IGNORE NULLS) OVER (ORDER BY TIMESTAMP)) as lastmodifieddate
from cte order by timestamp asc