如何在单个 SQL 语句中实现这一点

Question

请问我手头有问题，

我的数据库 MySQL 中有以下表格

students

studentID | fname   | mname | lname  |
1         | Wilson  | Dale  | Micheal|



examtype

examtypeID | name |
1          | ca 1
2          | ca 2
3          | ca 3
4          | exam


first_term_result

student_id | examtype_id | subject_id | mark
1          | 1           | 7          | 12
1          | 2           | 7          | 10
1          | 3           | 7          | 9
1          | 4           | 7          | 45

目前我有这个 SQL 语句

SELECT CONCAT(students.fname,' ',students.mname,' ',students.lname) 
    AS student_name, students.studentID, exam_type.name, first_term_result.mark 
    FROM students, exam_type, first_term_result 
    WHERE students.studentID=first_term_result.student_id 
    AND exam_type.exam_typeID=first_term_result.exam_type_id 
    AND first_term_result.subject_id=7

它的工作原理是我得到一个表，我可以用它来获取这样的数组

我是如何把它放到那个数组中的 使用 codeigniter 框架：

    $sheet = $this->teacher_model->spreadsheet(); 
    $data = array();
    foreach($sheet as $row)
    {
        $data[$row['student_name']]['studentID']=$row['studentID'];
        $data[$row['student_name']][$row['name']]=$row['mark'];

    }


Array
(
  [Wilson Dale Micheal] => Array
    (
        [studentID] => 1
        [CA 1] => 12
        [CA 2] => 10
        [CA 3] => 9
        [Exam] => 45
    )

)

另外一条SQL语句如下：

SELECT CONCAT(students.fname,' ',students.mname,' ',students.lname) 
    AS students_name, students.studentID, SUM(first_term_result.mark) as Total
    FROM students, first_term_result 
    WHERE students.studentID=first_term_result.student_id 
    AND first_term_result.subject_id=7 group by students_name

给出这样的东西：

Array
(
    [Wilson Dale Micheal] => Array
    (
        [studentID] => 1
        [Total] => 76
    )

)

合并两个数组得到我的结果，即：

这就是我合并两者的方式，函数 数组合并（） 没用所以我用了：

 $data = array();
    foreach($sheet as $row)
    {
        $data[$row['student_name']]['studentID']=$row['studentID'];
        $data[$row['student_name']][$row['name']]=$row['mark'];

    }

    foreach($total as $tol)
    {
        $data[$tol['student_name']]['Total']=$tol["Total"];
    }

Array
(
    [Wilson Dale Micheal] => Array
    (
        [studentID] => 1
        [CA 1] => 12
        [CA 2] => 10
        [CA 3] => 9
        [Exam] => 45
        [Total] => 76
    )

)

但是我想知道我是否可以通过一条 SQL 语句来实现所有这些，这样我就可以按总 DESC 进行排序，因此得分最高的学生将首先出现，依此类推。 尽管我拥有我想要的数组，但当前语句不会将 Total 排序为 DESC。

谢谢

Answer 1

SELECT CONCAT(s.fname,' ',s.mname,' ',s.lname) AS student_name,        
       MAX(s.studentID) As StudentID,
       e.name As Name, 
       SUM(f.mark) As Mark
FROM Students s 
JOIN First_Term_Result f ON s.studentID = f.student_id 
JOIN Exam_Type e ON e.examtypeID = f.examtype_id
WHERE f.subject_id=7
GROUP BY CONCAT(s.fname,' ',s.mname,' ',s.lname), e.name WITH ROLLUP;

根据您的样本数据得出的结果将是：

STUDENT_NAME    STUDENTID   NAME    MARK
Wilson Dale Micheal    1    ca 1    12
Wilson Dale Micheal    1    ca 2    10
Wilson Dale Micheal    1    ca 3    9
Wilson Dale Micheal    1    exam    45
Wilson Dale Micheal    1    (null)  76
(null)                 1    (null)  76

ROLLUP 增加了两行：

• 一个学生的总数（将为每个学生显示）
• 总计（所有学生一次）

如果您的 MySQL 版本支持 GROUPING 函数，您可以在“total”行中使用自己的标签而不是 NULL。

这里是SQL Fiddle，您可以通过修改表格内容进行测试。