无法从Codeigniter中的foreach循环中的两个表中获取记录

Question

I am working on Codeigniter and i have following tables, i want that first one subject name to be printed then all its sub-subjects and so on as given below :

Subjects:

-----------------------
id |     Subjects Name 
----------------------- 
1  |     Mathematics
2  |     Physics
3  |     Chemistry 

Subsections:

---------------------------------------------
id | subject_id    |   SubsectionsName
---------------------------------------------
1        2             Electromagnetism
2        1                 Algebra
3        3             Organic Chemistry
4        1           Geometry and Topology
5        2                 Mechanics

I want following output

Mathematics
 Algebra
 Geometry and Topology
Physics
 Electromagnetism
 Mechanics
Chemistry
 Organic Chemistry

for that i am using following code but it is not giving me correct output.

$condition = "id =" . "'" . $subject_id . "'";
$this->db->select('*');
$this->db->from('subject');
$this->db->where($condition);
$query = $this->db->get();

if ($query->num_rows() > 0) {

    foreach($query->result_array() as $row)
    {  
        $rows[] = $row;
        $condition = "subject_id =" . "'" . $row['id'] . "'";
        $this->db->select('*');
        $this->db->from('subsections');
        $this->db->where($condition);
        $query_course_material = $this->db->get();
        foreach($query->result_array() as $row1)
        {
          $rows[] = $row1;
        }

    }
    return $rows;

} else {
return false;
}

Answer 1

Inner foreach is having incorrect variable. It should have $query_course_material instead of $query. Please check below :

$query_course_material = $this->db->get();
foreach($query_course_material->result_array() as $row1)
{
   $rows[] = $row1;
}