na minha tabela de disciplinas, tenho todas as aulas dos alunos por semestre e mês, com pontos de cada mês

[
{
"id": "4", - this is the subject id
"userid": "1",
"name": "bio",
"semester": "3", - semester
"month": "5", - the month
"points": "652" - points of this class
"time": "2017-06-18 22:45:04"
},
{
"id": "3", - this is the subject id
"userid": "1",
"name": "math",
"semester": "3", - semester
"month": "4", - the month
"points": "33" - points of this class
"time": "2017-05-15 22:45:04"
},
{
"id": "2", - this is the subject id
"userid": "1",
"name": "chem",
"semester": "1", - semester
"month": "3", - the month
"points": "22" - points of this class
"time": "2017-04-11 22:45:04"
},
{
"id": "1", - this is the subject id
"userid": "1",
"name": "phy",
"semester": "1", - semester
"month": "2", - the month
"points": "10" - points of this class
"time": "2017-02-10 22:45:04"
}
]

isto é o que eu tentei

$sql = "SELECT users.id userid,users.name username,subjects.id subjectsid, subjects.name subjectname, subjects.points activepts FROM tbusers AS users INNER JOIN tbsubjects AS subjects ON users.id = subjects.userid WHERE users.id = '$userid' ORDER BY subjects.time DESC";

try {
    $db = new db();
    $db = $db->connect();
    $stmt = $db->prepare($sql);

$stmt->execute();

$user = $stmt->fetchAll(PDO::FETCH_OBJ);

$db = null;

if(empty($user)) {
    $response->getBody()->write
    ('
    {
        "error":
        {
            "message":"Invalid"
        }
    }');
} else {
    $response->getBody()->write(json_encode($user));
}
} catch(PDOException $e) {}

a saída atual que estou recebendo da minha consulta é várias respostas para cada uma por causa defetchAll eu poderia mudar parafetch mas não receberá os outros dados

[
{
"userid": "1",
"username": "joe",
"subjectid": "4",
"subjectname": "bio",
"activepts": "652"
},
"userid": "1",
"username": "joe",
"subjectid": "3",
"subjectname": "math",
"activepts": "33"
},
"userid": "1",
"username": "joe",
"subjectid": "2",
"subjectname": "chem",
"activepts": "22"
},
"userid": "1",
"username": "joe",
"subjectid": "1",
"subjectname": "phy",
"activepts": "10"
}
]

minha pergunta é como posso mesclá-los em uma resposta e retornar os dados abaixo na saída esperada (adicionei uma pequena descrição de cada campo para explicá-lo)

resultado esperado

[
{
"userid": "1", - from users table
"username": "joe",  - from users table 
"subjectsid": "1", - first subject id for the student in this case the one for phy
"subjectname": "bio", - current subject name 
"activepts": "652", - points of current month
"totalpts": "717", - total points of all subjects for this student
"sem1": "32", - total points of all subjects for this student of semester 1
"sem2": "0", - total points of all subjects for this student of semester 2
"sem3": "685", - total points of all subjects for this student of semester 3
}
]