不包括重复

Question

我坚持的查询应该列出员工销售的客户数量，并且只计算一次客户，即使他们有多个销售。我对此非常陌生，似乎无法弄明白。任何帮助是极大的赞赏！

select count(distinct o.customerid) 'Number of Customers',
e.EmployeeID 'Employee ID', e.LastName, e.firstname
from employees e
full join Orders o
on e.EmployeeID = o.employeeid
group by o.CustomerID, e.EmployeeID, e.LastName, e.firstname
order by e.employeeid, o.customerid asc

以下是我获得的结果，它表明了列表如何提供结果列表。我试图在一个字段中获取总数。希望这更有意义吗？

Answer 1

你的group by子句中有customerid - 所以它会为每个customerid生成一行 - 删除它（也来自orderby），也许你会得到你需要的结果

select count(distinct o.customerid) 'Number of Customers',
e.EmployeeID 'Employee ID', e.LastName, e.firstname
from employees e
full join Orders o
on e.EmployeeID = o.employeeid
group by  e.EmployeeID, e.LastName, e.firstname
order by e.employeeid