SQL联接另一个表

Question

我有一个查询学生分数表并返回其总分数，年级，注册号和分数排名（位置）的函数。我想编写一个Sql联接，该联接将使用分数表返回的注册号来获取来自学生表的学生姓名，但姓名不会返回，并且我没有收到任何错误。

public function get_subject_result(){

        $subjectID = $this->input->get('subjectID');
        $termID = $this->input->get('termID');
        $sessionID = $this->input->get('sessionID');

        //This Query which gave me headache actually ranks the total score and return positions
        //$this->db->query("JOIN student ON main.stud_reg = student.reg");
        $query = $this->db->query("SELECT (SELECT COUNT(*) + 1
            FROM result ref
            WHERE ref.total > main.total AND subject_id='".$subjectID."' AND term_id='".$termID."' AND session_id='".$sessionID."') as rank, ca1, ca2, exam,
            total, remark, stud_reg, grade, subject_id
            FROM result main JOIN student ON main.stud_reg = student.reg WHERE subject_id='".$subjectID."' AND term_id='".$termID."' AND session_id='".$sessionID."'
            ORDER BY total DESC");


        if ($query->num_rows() > 0) {
            return $query->result();
        }else{
            return false;
        }
    }