试图将两个不同的属性组合成一列

Question

我正在尝试编写一个显示 3 个不同列的查询。活动类别名称、总收入和客户数量。我下面的代码显示了这些列（以及 2 个不同的价格，学生价格和普通价格）。我要做的是编写一个查询，根据客户类型是什么来计算收入 * 适当的客户类型（学生或普通）。我似乎无法编写查询以将 2 种不同的客户类型和适当的价格区分开到“收入”列中。任何帮助将不胜感激！

SELECT ACTIVITY_NAME                                          AS CLASS,
       STUDENT_PRICE,
       REGULAR_PRICE,
       Count(CUSTOMER.CUSTOMER_TYPE)                          AS NUM_CUST,
       Count(CUSTOMER.CUSTOMER_TYPE) * ACTIVITY.STUDENT_PRICE AS REVENUE
FROM   ACTIVITY
       JOIN ACTIVITY_BOOKING
         ON ACTIVITY.ID = ACTIVITY_BOOKING.ACTIVITY_ID
       JOIN CUSTOMER
         ON ACTIVITY_BOOKING.CUSTOMER_ID = CUSTOMER.ID
GROUP  BY ACTIVITY_NAME,
          STUDENT_PRICE,
          REGULAR_PRICE
ORDER  BY ACTIVITY.ACTIVITY_NAME 

Answer 1

我认为您需要SUM 而不是COUNT，您可以将条件值求和为：

SELECT ACTIVITY_NAME                                          AS CLASS,
       STUDENT_PRICE,
       REGULAR_PRICE,
       Count(CUSTOMER.CUSTOMER_TYPE)                          AS NUM_CUST,
       Sum (case when CUSTOMER.CUSTOMER_TYPE = 'Student' then STUDENT_PRICE when CUSTOMER.CUSTOMER_TYPE = 'Regular' then REGULAR_PRICE else 0 end) AS REVENUE
FROM   ACTIVITY
       JOIN ACTIVITY_BOOKING
         ON ACTIVITY.ID = ACTIVITY_BOOKING.ACTIVITY_ID
       JOIN CUSTOMER
         ON ACTIVITY_BOOKING.CUSTOMER_ID = CUSTOMER.ID
GROUP  BY ACTIVITY_NAME,
          STUDENT_PRICE,
          REGULAR_PRICE
ORDER  BY ACTIVITY.ACTIVITY_NAME