找到最高的金額，盡管有不止一個達到相同的金額

Question

我想為每個國家找到最好的客戶，盡管一個國家有兩個客戶數量相同，我希望他們都出現。

select customerid,firstname,lastname,country, max(total_amt)
from (select invoice.customerid, customer.firstname,lastname, 
sum(invoice.total)total_amt,customer.country
  from invoice
   join customer
   on customer.customerid= invoice.customerid
   group by invoice.customerid,customer.country)t2
group by  country;

Answer 1

使用 window 函數：

select c.*
from (select c.country, c.customerid, c.firstname c.lastname, sum(i.total) as total,
             dense_rank() over (partition by c.country order by sum(i.total) desc) as seqnum
      from customer c join
           invoice i
           on c.customerid = i.customerid
     ) c
where seqnum = 1;

請注意，我還介紹了 window 函數，因此查詢更易於編寫和閱讀。