Question

当我运行第一个查询时，所有运行正常：

select uid,
(select top 1 city from UserData where UserData.uid = #uids.uid 
group by city)
from #uids;

问题是当我添加order by count(city)时，出现错误：由于内部错误，不支持此类型的相关子查询模式

select uid,
(select top 1 city from UserData where UserData.uid = #uids.uid 
group by city
order by count(city))
from #uids;

Answer 1

该错误表明您的子查询不起作用，这是显而易见的，因为您不能在ORDER子句中使用SQL函数。您只能在SELECT和HAVING子句中使用它们。

如果要按count(city)排序，则应将其添加到带有别名的SELECT子句，并按别名命令。所以你的子查询可以是这样的：

(SELECT city, COUNT(*) AS city_count
FROM UserData
WHERE UserData.uid = #uids.uid
GROUP BY city
ORDER BY city_count
LIMIT 1)

Answer 2

我会在RedShift中使用row_number()执行此操作：

select u.uid, ud.city
from uids u left join
     (select uid, city, count(*) as cnt,
             row_number() over (partition by uid order by count(*) desc) as seqnum
      from UserData ud
      group by uid, city
     ) ud
     on ud.uid = u.uid and seqnum = 1;

您也可以在SQL Server中尝试此操作。

由于内部错误，不支持Redshift这种类型的相关子查询模式

2 个答案: