[英]How to achive this in a single SQL statement
请我手头有问题,
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
它在我得到一个表时可以工作,在这里我可以用来获取这样的数组
我如何使用codeigniter框架将其放入该数组 :
$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
)
)
另一个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
)
)
合并两个数组我得到我的结果,这是:
这是我合并合并两者的方式,函数array_merge()没有起作用,所以我使用了:
$data = array();
foreach($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
)
)
但是我想知道是否可以用一个SQL语句实现所有这些目标,以便我能够使ORDER BY Total DESC,所以得分最高的学生将排在首位,依此类推。 尽管我有想要的数组,但当前语句不会将Total排序为DESC。
谢谢
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
添加了两行:
如果您的MySQL版本支持GROUPING
功能,则“总计”行中可以有自己的标签,而不是NULL。
这是SQL Fiddle ,您可以在其中通过修改表内容进行测试。
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