Codeigniter: having issue with fetching data as sum of columns - codeigniter

Question

i am new to Codeigniter, i have two tables named as Users and Amount, there are multiple amounts in Amount Table across one user have same user_id which is foreign key. i want to get data and sum up the amounts value if user_id is same.
My Modal is:
public function client_list(){
$this->db->select_sum('*', sum('amount'));
$this->db->from('users');
$this->db->join('amount', 'amount.user_id = users.ID');
$query=$this->db->get();
$result=$query->result();
return $result;
}
Controller is:
public function index(){
$data['records'] = $this->Admin_model->client_list();
$this->load->view('admin/Client_list', $data);
}
View part is:
<?php
foreach($records as $record):
?>
<tr class="odd gradeX">
<td>
<label class="mt-checkbox mt-checkbox-single mt-checkbox-outline">
<input type="checkbox" class="checkboxes" value="1" />
<span></span>
</label>
</td>
<td> <?php echo $record->firstname; ?> </td>
<td> <?php echo $record->lastname; ?> </td>
<td> <?php echo $record->phone;?> </td>
<td> <?php echo $record->email;?> </td>
<td> <?php echo $record->amount;?> </td>
<td> <?php echo $record->dateofbirth;?> </td>
</tr>
<?php endforeach; ?>
Kind Help would be highly appreciated.