SQL-在未定义的间隔内查询记录

Question

我需要使用SQL（确切地说是SQL Server）从Northwind数据库的Orders表中获取以下数据：

• 查找在6个月内（ OrderDate ）至少下了3个订单的所有客户（ CustomerID ）。

因此，对于以下数据，查询应返回1

==========================
| CustomerID | OrderDate |
==========================
|      1     | 2000-1-1  |
--------------------------
|      1     | 2000-1-5  |
--------------------------
|      1     | 2000-4-30 |
--------------------------
|      2     | 2000-1-1  |
--------------------------
|      2     | 2000-5-30 |
--------------------------

Answer 1

SELECT N1.CustomerID, COUNT(N2.OrderDate)  FROM Northwind N1
INNER JOIN Northwind N2
ON N1.CustomerID=N2.CustomerID
AND N1.OrderDate<=Dateadd(MONTH, 6, N2.OrderDate)
GROUP BY N1.CustomerID
HAVING COUNT(N2.OrderDate)>=3

Answer 2

请尝试以下操作：

SELECT OrderDate, CustomerID FROM orders GROUP BY OrderDate HAVING   COUNT(CustomerID) >= 3 ORDER BY COUNT(CustomerID) DESC