MySql : 如何跳过子查询中的连接

Question

我写了一个关于查找在法国和德国销售的产品的程序。另一方面，我对我的子查询不满意。我有一种感觉，所有的连接都可以被跳过并且完成得更快，但我找不到这个问题的答案。

代码如下：

select productname 
from products p 
join [Order Details] od on p.productid = od.ProductID 
join orders o on od.OrderID = o.OrderID 
join customers c on o.CustomerID = c.CustomerID
where p.ProductID in (select p.productid 
                      from products p 
                      join [Order Details] od on p.productid = od.ProductID 
                      join orders o on od.OrderID = o.OrderID 
                      join customers c on o.CustomerID = c.CustomerID 
                      where c.Country LIKE 'France')
  and p.ProductID in (select p.productid 
                      from products p 
                       join [Order Details] od on p.productid = od.ProductID 
                       join orders o on od.OrderID = o.OrderID 
                       join customers c on o.CustomerID = c.CustomerID 
                       where c.Country  LIKE 'Germany')
group by productname

所以我要求的是尽可能地简化它，但是以基本的方式，或者展示跳过连接等的方法。

https://i.stack.imgur.com/UWlzn.png

Answer 1

select productname 
from products p 
join [Order Details] od on p.productid=od.ProductID 
join orders o on od.OrderID=o.OrderID 
join customers c on o.CustomerID=c.CustomerID
where c.Country in ('France', 'Germany') 
group by productname 
having COUNT(DISTINCT c.Country) = 2;

MySql : 如何跳过子查询中的连接

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