Exasol中的相关子查询

Question

我尝试在Exasol数据库中使用SQL编写一个子查询。这个问题类似于这个线程(SQL Query - join on less than or equal date)，代码在mysql和postgres中运行良好。但是，当我将代码移到Exasol时，它显示SQL Error 42000: correlation in on子句。我想知道是否有任何替代方案来解决这个问题，或者我如何在Exasol中解决它？

    SELECT a.ID, 
           a.join_date,
           a.country, 
           a.email,
           b.start_date,
           b.joined_from
      FROM a 
 LEFT JOIN b 
        ON a.country = b.country 
       AND b.start_date = (
           SELECT MAX(start_date) 
             FROM b b2 
            WHERE b2.country = a.country 
              AND b2.start_date <= a.join_date
           );

Answer 1

尽管Exasol上不支持相关查询，但可以使用DENSE_RANK() SQL function解决此要求，如下所示

with cte as (
        select
               a.ID, a.join_date, a.country, a.email, b.start_date, b.joined_from,
               dense_rank() over (partition by b.country order by b.start_date desc) r1
        from a
        left join b
                on a.country = b.country
)
select * from cte where r1 = 1