how to calculate the sum of grades for each student - php

Question

I have one table for the grades of exams, and another for students (the students table will always have 10 students only).
I want to output an array in Json format for students details with the sum of grades of each by semester in array of array.
expected output
[
{
"id": "1", -> this is the semester ID
"student1": {"id": "1","name": "student name", "bio": "50", "chem": "50", "math": "60", "total grades": "160"},
"student2": {"id": "2","name": "secondstudent name", "bio": "60", "chem": "60", "math": "50", "total grades": "170"},
}
]
here is my tables structure
tbStudents
id , name
1 , student name
2 , secondstudent name
3 , thirdstudent name
tbGrades
id , student , semster , bio , chem , math , total
1 , 1 , 1 , 50 , 50 , 60 , 160
2 , 2 , 1 , 30 , 40 , 20 , 90
3 , 2 , 1 , 30 , 20 , 30 , 80
challenge
How to calculate the SUM of each bio, chem, math, total for each student by semester, cause the student might have multiple grades in the same semester
what i've tried
$sql = "SELECT grade.id g_id, grade.semester g_semester, grade.bio g_bio, grade.chem g_chem, grade.math g_math, grade.total g_total, student.id s_id, student.name s_name FROM tbGrades AS grade INNER JOIN tbStudents AS student ON student.id = grade.student";
try {
$db = new db();
$db = $db->connect();
$stmt = $db->prepare($sql);
$stmt->execute();
$grade = $stmt->fetchAll(PDO::FETCH_OBJ);
$db = null;
if(empty($grade)) {
$response->getBody()->write
('
{
"error":
{
"status":"400",
"message":"Invalid Request"
}
}');
} else {
foreach($grade as $value) {
$array_resp[]=[
'id' => $value->g_id,
'student1' => ['id'=>$value->s_id, 'name'=>$value->s_name, 'bio'=>$value->g_bio, 'chem'=>$value->g_chem, 'math'=>$value->g_math, 'total grades'=>$value->g_total],
];
}
$response->getBody()->write(json_encode($array_resp));
}
} catch(PDOException $e) {
$response->getBody()->write
('
{
"error":
{
"message":'. $e->getMessage() .'
}
}');
}

Answer 1

You can do it easily using MySQL GROUP BY clause.
SELECT
grade.id g_id,
grade.semester g_semester,
SUM(grade.bio) g_bio,
SUM(grade.chem) g_chem,
SUM(grade.math) g_math,
SUM(grade.total) g_total,
student.id s_id,
student.name s_name
FROM
tbGrades AS grade
INNER JOIN
tbStudents AS student
ON
student.id = grade.student
GROUP BY
student.id,
grade.semester