添加一列，该列根据2007年期间的订单数量确定回头客的频率

Question

该列应包含：  计数= 0的“无订单”计数= 1的“一次性”计数范围2-5的“常规”计数范围6-10的“经常”计数大于10的“忠诚”

下面是查询，在这里我无法使用其他条件，例如“大于范围”

SELECT c.CustomerID, c.TerritoryID,
COUNT(o.SalesOrderid) [Total Orders],
CASE COUNT(o.SalesOrderid)
WHEN 1 
THEN 'One Time' 
WHEN 0
THEN 'No Order'
ELSE 'None' 
END AS [Frequency]  
FROM Sales.Customer c
LEFT OUTER JOIN Sales.SalesOrderHeader o
ON c.CustomerID = o.CustomerID
WHERE DATEPART(year, OrderDate) = 2007
GROUP BY c.TerritoryID, c.CustomerID;

我的输出截图

Answer 1

您可以使用documentation中所述的搜索格式，而不是简单的CASE表达式，如下例所示。另外，我建议您避免将DATEPART函数应用于OrderDate中的WHERE并按如下所示进行重构，以便表达式可修改，从而可以有效地使用索引。

SELECT
      c.CustomerID
    , c.TerritoryID
    , COUNT(o.SalesOrderid) [Total Orders]
    , CASE 
        WHEN COUNT(o.SalesOrderid) = 0 THEN 'No Order'
        WHEN COUNT(o.SalesOrderid) = 1 THEN 'One Time' 
        WHEN COUNT(o.SalesOrderid) BETWEEN 2 AND 5 THEN 'Regular'
        WHEN COUNT(o.SalesOrderid) BETWEEN 6 AND 10
        THEN 'Often'
        ELSE 'Loyal' 
    END AS [Frequency]  
FROM Sales.Customer c
LEFT OUTER JOIN Sales.SalesOrderHeader o
ON c.CustomerID = o.CustomerID
WHERE OrderDate >= '20070101' AND OrderDate < '20080101'
GROUP BY c.TerritoryID, c.CustomerID;