准备月度销售报告谁拥有最大的销售客户，为下表

Question

准备谁拥有最大的销售客户的月度销售报告，为下表

Answer 1

这是如何你可以在“一”查询检索一个例子：

• 谁拥有最大的销售客户的ID
• 该客户的销售汇总

首先带来的CUSTOMER_ID和销售的相应的总结查询是这样的：

select customer_id, sum(sales) as sumsales from mytable group by customer_id; 

这个疑问，等级已被添加到销售摘要的降序排列。这将允许稍后根据其等级选择单个记录。因此，一个包装是必要的：

select customer_id, sumsales, rank() over (order by sumsales desc) as rnk from 
    (select customer_id, sum(sales) as sumsales from mytable group by customer_id); 

现在的排名条目是可用的，排名第一的记录，必须选择：

select customer_id, sumsales from 
    (select customer_id, sumsales, rank() over (order by sumsales desc) as rnk from 
     (select customer_id, sum(sales) as sumsales from mytable group by customer_id) 
    ) 
where rnk=1; 

然而，这未必是实现最有效的方法这个。

编辑：

为了避免一个包裹层，只是添加的等级，有可能秩foeld添加到第一内部查询：

select customer_id, sum(sales) as sumsales, rank() over (order by sum(sales) desc) as rnk 
from mytable group by customer_id; 

然后，单个需要包装的查询，选择排名第一的记录为：

select customer_id, sumsales from (
    select customer_id, sum(sales) as sumsales, rank() over (order by sum(sales) desc) as rnk 
    from mytable group by customer_id 
) 
where rnk=1; 

参考其他类似的相关答案here。