Database

My database tbl_user has the following columns :

    | User_id | Upline | Right_id | Left_id |
    +--------+---------+----------+---------+
    | 1      | 0       |   4      | 7       |
    | 2      | 0       |   6      | 5       |
    | 3      | 0       |   0      | 0       |
    | 4      | 1       |   0      | 0       |
    | 5      | 2       |   0      | 0       |
    | 6      | 2       |   0      | 0       |
    | 7      | 1       |   0      | 0       |
    | 8      | 0       |   0      | 0       |
    | 9      | 0       |   0      | 0       |
    | 10     | 0       |   0      | 0       |  
    +--------+---------+----------+---------+

    $user_id = 2;
    
    $user_tree = $this->getAllRec("u.user_id",  
    "tbl_user u",
    "WHERE u.Upline = '".$user_id."'
    ORDER BY Right_id ASC");
    
    print_r($user_tree);

I want the array `$user_tree` to hold (user_id 5) first, then (user_id 6), how to do that?

I want to print **Left_id** first, then only print **Right_id**. May I know how to do it?

Do I need to use left join or use another query?

public class Teacher
{
        public string Id{ get; set; }
        public string Name{ get; set; }
        public string TeacherFilter{ get; set; }
        ...
}

public class Student
{
        public string Id{ get; set; }
        public string Name{ get; set; }
        public string StudentFilter{ get; set; }
        public string TeacherId{ get; set; }
        ...
}

public class TeacherStudents
{
        public string Id{ get; set; } -- from teacher
        public string Name{ get; set; } -- from teacher
        public IEnumerable<Student> Students{get;set;}
}

public class TeacherStudents
{
        public string Id{ get; set; } -- from teacher
        public string Name{ get; set; } -- from teacher
        public IEnumerable<Student> Student{get;set;}
}

public class TeacherStudent
{
        public string Id{ get; set; } -- from teacher
        public string Name{ get; set; } -- from teacher
        ...
        public Student Student{get;set;}
}

Get(string TeacherFilter,string StudentFilter).

var query = teacherCollection.Aggregate().Match(x => x.TeacherFilter== TeacherFilter); //filter teach
var query1 = query
.Lookup<Teacher, Student, TeacherStudent>(studentCollection, t => t.Id, s => s.TeacherId, l => l.Student)
.Unwind(x => x.Student, new AggregateUnwindOptions<TeacherStudent>())
.Match(x => x.StudentFilter== StudentFilter) //filter student   

mysql> SELECT username,score,level, FIND_IN_SET(score,(SELECT GROUP_CONCAT(score ORDER BY score ASC)FROM highscore WHERE game = 0 AND level = 4 AND user = 10 )) AS rank FROM highscore WHERE game = 0 AND level = 4 AND user = 1 ORDER BY rank LIMIT 10;