Question

我有一个简单的查询来获取创建交易时使用的货币汇率：

SELECT t.orderid, t.date, 
 (SELECT rate FROM sources.currency_rates r WHERE currencyid=1 AND 
r.date>=t.date  ORDER BY date LIMIT 1) rate
FROM sources.transactions t

这会触发错误：

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

我尝试了几种类型的连接和命名子查询，但似乎都没有。完成此任务的最佳方法是什么？看起来像一个非常常见的场景，应该在BQ的标准Sql中实现起来非常简单。

Answer 1

以下是BigQuery Standard SQL

String oldstring = "2011-01-18 00:00:00";
LocalDateTime datetime = LocalDateTime.parse(oldstring, DateTimeFormatter.ofPattern("YYYY-MM-DD HH:MM:SS"));

Answer 2

我注意到与其他相关子查询的类似行为。它们很有用，但不能总是通过BigQuery自动建模为JOIN。

类似的案例有效：

#standardSQL
SELECT name, (
  SELECT AVG(temp) 
  FROM `bigquery-public-data.noaa_gsod.gsod2017` b
  WHERE a.usaf=b.stn  
) temp
FROM `bigquery-public-data.noaa_gsod.stations` a
LIMIT 10

不能工作：

#standardSQL
SELECT name, (
  SELECT temp 
  FROM `bigquery-public-data.noaa_gsod.gsod2017` b
  WHERE a.usaf=b.stn  
  ORDER BY da 
  LIMIT 1
) temp
FROM `bigquery-public-data.noaa_gsod.stations` a
LIMIT 10

修正：

#standardSQL
SELECT name, ARRAY_AGG(temp ORDER BY da LIMIT 1) temp
FROM `bigquery-public-data.noaa_gsod.stations` a
JOIN `bigquery-public-data.noaa_gsod.gsod2017` b
ON a.usaf=b.stn  
GROUP BY 1
LIMIT 10

（给我一个公共数据集，我将编写一个与您的数据一起使用的查询）

避免BigQuery中的相关子查询错误

2 个答案: