我正在尝试从外部查询的每一行获取concat列表，但在Unknown column 'outter_client' in 'where clause'其他地方，我看到您无法从子查询访问外部变量，有没有一种方法可以在没有存储过程，视图或临时条件的情况下重新构造此查询表并使其正常工作？
SELECT client AS outer_client, top_domain
FROM log
JOIN (
SELECT GROUP_CONCAT(t.domain) AS top_domain
FROM (
SELECT domain
FROM log
WHERE client = outer_client
GROUP BY 1
ORDER BY SUM(bytes)
LIMIT 5
) t
) k
GROUP BY client
ORDER BY SUM(bytes)
LIMIT 5;
我认为您需要基于字节数的每个客户端的前五个域。您可以使用嵌套选择和substring_index()/group_concat()技巧来做到这一点：
select client,
substring_index(group_concat(domain order by sumbytes desc), ',', 5) as top5domains
from (select client, domain, sum(bytes) as sumbytes
from log
group by client, domain
) cd
group by client
order by sum(sumbytes) desc
limit 5;
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