带有 SELECT 子查询的 BigQuery COALESCE()

Posted 2023-03-25

【中文标题】带有 SELECT 子查询的 BigQuery COALESCE()

【英文标题】：BigQuery COALESCE() with SELECT subquery

【发布时间】：2018-02-27 20:22:58

【问题描述】：

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

关于以下查询

(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)

我实际上是在尝试用查找表中的另一个 custom_id 替换 null custom_ids。有没有更好的方法可以让 BigQuery 接受？

【参考方案1】：

只需使用常规的 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