MySQL 从查询结果中添加列

Question

我想 add/create 基于此特定列结果的 table 列中的三列。这是我在 tblexammarks 中的记录：

SELECT exm.ID, 
       exm.Admission_No, 
       exm.Subject AS 'SID', 
       sb.Name AS 'Subject Name', 
       exm.Term, 
       exm.Test, 
       exm.Marks 
FROM tblexammarks exm 
INNER JOIN tblsubjects sb ON exm.Subject=sb.ID 
ORDER BY exm.ID ASC;

输出：

ID  Admission_No  SID  Subject Name  Term      Test       Marks 
1   KBA-2022-003   6   Science       Term One  Test One   94
2   KBA-2022-003   6   Science       Term One  Test Two   88
3   KBA-2022-003   6   Science       Term One  Test Three 78

这是我想要实现的目标：

Admission_No  SID  Subject Name  Term      Test One  Test Two  Test Three Total Marks       
KBA-2022-003   6   Science       Term One  94        88        78         260

我试过的和输出：

SELECT exm.ID, 
       exm.Admission_No, 
       exm.Subject AS 'SID', 
       sb.Name AS 'Subject Name', 
       exm.Term, 
       if(Test='Test One', marks, 0) AS 'Test One', 
       if(Test='Test Two', marks, 0) AS 'Test Two', 
       if(Test='Test Three', marks, 0) AS 'Test Three'
FROM tblexammarks exm 
INNER JOIN tblsubjects sb ON exm.Subject=sb.ID;

ID  Admission_No  SID  Subject Name  Term      Test One  Test Two  Test Three   
1   KBA-2022-003  6    Science       Term One  94        0         0
2   KBA-2022-003  6    Science       Term One  0         88        0
3   KBA-2022-003  6    Science       Term One  0         0         78

我试过使用 MySQL IF 函数，但我迷路了。有人可以帮忙吗

Answer 1

您可以尝试使用条件语句 IF 并为三个 Test 字段中的每一个提取单个值，然后使用 MAX 聚合函数删除空值和 SUM 以获得 Marks 字段的总计，然后使用 GROUP BY 子句聚合其余选定字段。

SELECT exm.Admission_No, 
       exm.Subject                                          AS SID, 
       sb.Name                                              AS Subject_Name, 
       exm.Term, 
       MAX(IF(exm.Test = 'Test One'  , 'Test One'  , NULL)) AS Test_One, 
       MAX(IF(exm.Test = 'Test Two'  , 'Test Two'  , NULL)) AS Test_Two, 
       MAX(IF(exm.Test = 'Test Three', 'Test Three', NULL)) AS Test_Three, 
       SUM(exm.Marks)                                       AS Marks
FROM       tblexammarks exm 
INNER JOIN tblsubjects sb 
        ON exm.Subject = sb.ID 
GROUP BY exm.Admission_No, 
         exm.Subject AS 'SID', 
         sb.Name AS 'Subject Name', 
         exm.Term
ORDER BY exm.ID ASC;

如果您能提供两个表中的示例数据，我可以提供经过全面测试的解决方案。

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