带有SELECT子查询的BigQuery COALESCE（）

Question

我收到错误：

Correlated subqueries that reference other tables are not supported unless they can be de-correlated, such as by transforming them into an efficient JOIN

在以下查询

上

(SELECT DISTINCT video_id, 
                   COALESCE(custom_id, 
                             (SELECT custom_id FROM `test2.channel_map` b 
                              WHERE a.channel_id = b.channel_id LIMIT 1), 
                                'Default')
 FROM `test2.revenue` a)

我实际上是在尝试将null custom_ids替换为查找表中的另一个custom_id。有没有比BigQuery更好的方法可以接受？

Answer 1

只需使用常规LEFT JOIN - 如下所示

  

SELECT DISTINCT video_id, 
  COALESCE(
    a.custom_id, 
    b.custom_id, 
    'Default'
  )
FROM `test2.revenue` a
LEFT JOIN `test2.channel_map` b
ON a.channel_id = b.channel_id