SQL-在未定義的間隔內查詢記錄

Question

我需要使用SQL（確切地說是SQL Server）從Northwind數據庫的Orders表中獲取以下數據：

• 查找在6個月內（ OrderDate ）至少下了3個訂單的所有客戶（ CustomerID ）。

因此，對於以下數據，查詢應返回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

請嘗試以下操作：

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