1

我有以下表格：

交易： Transaction_ID Datetime Giver_ID Recipient_ID Points Category_ID Reason

奖励： Reward_ID Title Description Image_URL Date_Inactive Stock_Count Cost_to_User Cost_to_System

采购：Purchase_ID Datetime Reward_ID Quantity Student_ID Student_Name Date_DealtWith Date_Collected

工作人员奖励学生积分，这些积分将成为交易表的条目，如下所示：

Transaction_ID Datetime Giver_ID Recipient_ID Points Category_ID Reason
8 2011-09-07 36761 127963 2 1 Excellent behaviour in behaviour unit

然后，学生可以购买成为购买表条目的奖励，如下所示：

Purchase_ID Datetime Reward_ID Quantity Student_ID Student_Name Date_DealtWith Date_Collected
1570 2012-05-30 12:46:36 2 1 137616 Bradley Richardson NULL NULL

所有奖励都手动存储在奖励数据库表中：

Reward_ID Title Description Image_URL Date_Inactive Stock_Count Cost_to_User Cost_to_System
1 Lunch Time Queue Pass (month) Beat the queue and get to the hot food early! /user/74/167976.png 2012-04-16 11:50:00 0 100 0

我的问题是这样的：

我可以使用什么 SQL 语句来返回Student Name、Points Earned、Points Spent、Points Remaining？

不久前我问了一个类似的问题，它提供了以下陈述。但是，经过检查，它似乎并不完全准确 - 特别是所用积分无法正常工作。

SELECT  Recipient_ID AS StudentID,
        SumOfPointsOfPurchasesMade.Points AS PurchasesMade,
        SumOfPointsEarned.Points AS PointsEarned,
        SumOfPointsEarned.Points - COALESCE(SumOfPointsOfPurchasesMade.Points, 0) AS CurrentPoints
FROM   
(
    SELECT SUM(Points) AS Points, Recipient_ID 
    FROM   transactions
    GROUP  BY Recipient_ID
) AS SumOfPointsEarned 
    LEFT JOIN 
    (
        SELECT purchases.Student_ID,  SUM(rewards.Cost_to_User) AS Points 
        FROM   purchases 
            INNER JOIN rewards 
            ON purchases.Reward_ID = rewards.Reward_ID
        GROUP  BY purchases.Student_ID
    ) AS SumOfPointsOfPurchasesMade 
    ON SumOfPointsEarned.Recipient_ID = SumOfPointsOfPurchasesMade.Student_ID
WHERE SumOfPointsEarned.Points < SumOfPointsOfPurchasesMade.Points
ORDER BY `CurrentPoints`  DESC

提前致谢，

4

2 回答 2

3

您只需要使用外连接来组合表格，然后按学生分组：

SELECT purchases.Student_Name                               AS `Student Name`,
       SUM(transactions.Points)                             AS `Points Earned`,
       SUM(rewards.Cost_to_User)                            AS `Points Spent`,
       SUM(transactions.Points) - SUM(rewards.Cost_to_User) AS `Points Remaining`
FROM   transactions
  LEFT JOIN purchases ON purchases.Student_ID = transactions.Recipient_ID
  LEFT JOIN rewards   USING (Reward_ID)
GROUP BY purchases.Student_ID
ORDER BY `Points Remaining` DESC
于 2012-07-04T11:23:29.643 回答
1

我愚蠢地意识到另一篇文章中的一个小错误解决了我遇到的问题：

SELECT SumOfPointsEarned.Points - COALESCE(SumOfPointsOfPurchasesMade.Points, 0) AS CurrentPoints
FROM   
(
    SELECT SUM(Points) AS Points, Recipient_ID 
    FROM   transactions 
            WHERE Recipient_ID= 137642
    GROUP  BY Recipient_ID
) AS SumOfPointsEarned 
    LEFT JOIN 
    (
        SELECT purchases.Student_ID,  SUM(rewards.Cost_to_User * purchases.Quantity) AS Points 
        FROM   purchases 
            INNER JOIN rewards 
            ON purchases.Reward_ID = rewards.Reward_ID 
                    WHERE Student_ID = 137642
        GROUP  BY purchases.Student_ID
    ) AS SumOfPointsOfPurchasesMade 
    ON SumOfPointsEarned.Recipient_ID = SumOfPointsOfPurchasesMade.Student_ID
ORDER BY CurrentPoints ASC

这一行是问题所在：

SUM(rewards.Cost_to_User * purchases.Quantity) AS Points

没有数量的乘法。嗬！

于 2012-07-04T11:57:02.767 回答