AWS Athena中的嵌套查询替代方案

时间:2017-01-24 15:33:52

标签: sql amazon-web-services presto amazon-athena

我正在运行一个查询,该查询提供了一组非重叠的first_party_id&id,它们与一个第三方相关联,但与另一个第三方相关联。但是,此查询不在Athena中运行,而是出现错误:Correlated queries not yet supported.

正在查看prestodb文档,https://prestodb.io/docs/current/sql/select.html(Athena是引擎盖下的prestodb),用于替代嵌套查询。给出的with statement示例似乎没有很好地转换为此not in子句。想知道嵌套查询的替代方法是什么 - 在下面查询。

SELECT 
         COUNT(DISTINCT i.third_party_id) AS uniques
FROM 
         db.ids i
WHERE
         i.third_party_type = 'cookie_1'
         AND i.first_party_id NOT IN (
           SELECT
             i.first_party_id
           WHERE 
             i.third_party_id = 'cookie_2'
         )

2 个答案:

答案 0 :(得分:7)

可能有更好的方法来做到这一点 - 我很想看到它!我能想到的一种方法是使用外连接。 (我不确定你的数据是如何构建的,所以请原谅这个人为的例子,但我希望它可以翻译好。)这个怎么样?

with 
  a as (select * 
       from (values 
       (1,'cookie_n',10,'cookie_2'), 
       (2,'cookie_n',11,'cookie_1'),
       (3,'cookie_m',12,'cookie_1'),
       (4,'cookie_m',12,'cookie_1'),
       (5,'cookie_q',13,'cookie_1'),
       (6,'cookie_n',13,'cookie_1'),
       (7,'cookie_m',14,'cookie_3')
       ) as db_ids(first_party_id, first_party_type, third_party_id, third_party_type)
      ),
  b as (select first_party_type 
        from a where third_party_type = 'cookie_2'),
  c as (select a.third_party_id, b.first_party_type as exclude_first_party_type 
        from a left join b on a.first_party_type = b.first_party_type 
        where a.third_party_type = 'cookie_1')
select count(distinct third_party_id) from c 
       where exclude_first_party_type is null;

希望这有帮助!

答案 1 :(得分:0)

您可以使用外部联接:

SELECT 
         COUNT(DISTINCT i.third_party_id) AS uniques
FROM 
         db.ids a
LEFT JOIN
         db.ids b
ON       a.first_party_id = b.first_party_id
     AND b.third_party_id = 'cookie_2'
WHERE
         a.third_party_type = 'cookie_1'
     AND b.third_party_id is null -- this line means we select only rows where there is no match

在将NOT IN用于可能返回NULL值的子查询时,您也应该小心,因为条件将始终为true。您的查询正在将a.first_party_idNULL进行比较,这将始终为false,因此NOT IN将导致条件始终为true。讨厌的小陷阱。

避免这种情况的一种方法是避免使用NOT IN或向子查询中添加条件,即AND third_party_id IS NOT NULL

有关详细说明,请参见here