SQL使用Count和Group By

Question

我必须根据State及其最近的订单选择客户总数，即DateFilled。

select CustomerLastName,CustomerFirstName, [State], DateFilled from customer


State  Total#CustByState    RecentDateFilled 
CA        100                04/01/2014
AZ        80                 04/23/2014
OR        120                02/02/2014

Answer 1

简单分组会为您提供计数和最新订单，当然这是该州任何客户的最新订单？

SELECT [State], COUNT(*) as TotalCusts, Max(DateFilled) as LastDateFilled
FROM Customer
GROUP By State;

如果您需要不同客户的数量（假设您桌子上的其他位置有一些关键字）：

SELECT [State], COUNT(DISTINCT CustId) as TotalCusts, Max(DateFilled) as LastDateFilled
FROM Customer
GROUP By State;