根据计算值进行选择，优化

Question

我需要在其他领域中选择客户在购买特定品牌产品等时的年龄，例如客户在30到50岁之间。我写了这个查询（getAge只使用DATEDIFF来以年为单位返回年龄）

SELECT DISTINCT customers.FirstName, customers.LastName, 
             products.ProductName,
             dbo.getAge(customers.BirthDate,sales.Datekey)
              AS Age_when_buying
FROM sales
 INNER JOIN dates ON sales.Datekey=dates.Datekey
 INNER JOIN customers ON sales.CustomerKey=customers.CustomerKey
 INNER JOIN products ON sales.ProductKey=products.ProductKey
 INNER JOIN stores ON sales.StoreKey=stores.StoreKey

WHERE stores.StoreName = 'DribleCom Europe Online Store' AND
products.BrandName = 'Proseware' AND
dbo.getAge(customers.BirthDate, sales.Datekey) >= 30 AND
dbo.getAge(customers.BirthDate, sales.Datekey) <=50

它工作，但我计算年龄三次。我试图将age_when_buying分配给一个变量，但它没有工作。我接下来的想法是使用光标，但我觉得有一个更简单的方法，我失踪。问题是：这是解决这个问题的合适方式或者我的选择是什么？

Answer 1

假设您只需要应用有限数量的过滤器，则可以使用公用表表达式重新构建查询。

我个人觉得在一个地方看到所有连接更容易，而过滤器在底部类似地组合在一起...

WITH CTE AS(
    select customers.FirstName
         , customers.LastName
         , dbo.getAge(customers.BirthDate,sales.Datekey) AS Age_when_buying
         , sales.StoreName
         , products.BrandName
         , products.ProductName
    from sales
         INNER JOIN customers on sales.CustomerKey=customers.CustomerKey
         INNER JOIN products ON sales.ProductKey = products.ProductKey
         INNER JOIN stores ON sales.StoreKey = stores.StoreKey
)
SELECT DISTINCT FirstName, LastName, ProductName, Age_when_buying
FROM CTE
WHERE StoreName = 'DribleCom Europe Online Store'
  AND BrandName = 'Proseware'
  AND Age_when_buying BETWEEN 30 AND 50

Answer 2

您应该使用Cross Apply。

SELECT DISTINCT customers.FirstName, customers.LastName, 
             products.ProductName,
             age.age AS Age_when_buying
FROM sales
 INNER JOIN dates ON sales.Datekey=dates.Datekey
 INNER JOIN customers ON sales.CustomerKey=customers.CustomerKey
 INNER JOIN products ON sales.ProductKey=products.ProductKey
 INNER JOIN stores ON sales.StoreKey=stores.StoreKey
CROSS APPLY
(select dbo.getAge(customers.BirthDate, sales.Datekey) as age) age
WHERE stores.StoreName = 'DribleCom Europe Online Store' AND
products.BrandName = 'Proseware' AND
age.age >= 30 AND
age.age <=50

Answer 3

您可以使用WITH子句：

WITH Customers_Info (CustomerFirstName, CustomerLastName, CustomerKey, AgeWhenBuying)
AS
(
    SELECT customers.FirtName,
           customers.LastName,
           CustomerKey
           dbo.getAge(customers.BirthDate, sales.DateKey) As AgeWhenBuying
    FROM customers
    JOIN sale USING(CustomerKey)
)
SELECT FirstName,
       LastName,
       products.ProductName,
       Customers_Info.AgeWhenBuying
    FROM Customers_Info
    JOIN sale USING(CustomerKey)
    JOIN products USING(ProductKey)
    JOIN stores USING(StoreKey)
    WHERE stores.StoreName = 'DribleCom Europe Online Store'
      AND products.BrandName = 'Proseware'
      AND Customers_Info.AgeWhenBuying >= 30
      AND Customers_Info.AgeWhenBuying <= 50;