Why does a CodeIgniter update() with no WHERE clause update all rows with the same data?

I am trying to update a specific row of a table in CodeIgniter, but my code update all rows!

Model:

public function edit_profile($array)
{
    $email = $array['email'];
    $this->db->select("email");
    $this->db->from("user");
    $this->db->where('email', $email);
    $query=$this->db->get();
    if ($query->num_rows() == 1) {
        $this->db->update('user', $array);
        return 1;
    } else {
        return $query->num_rows(); 
    }
}

Controller:

public function edit()
{
    $name = $this->input->post('user_name', TRUE);
    $email = trim($this->session->userdata('email'));
    $array = array('user_name' => $name, 'email' => $email);
    $result = $this->edit_profile_model->edit_profile($array);
    echo $result;
}

And in new page it show the echo value 1.
How to update specific row?
Why does $query->num_rows() return 1 and update all rows?

Try using a where condition to update a specific record

$updateData = [
   'user_name' => $array['user_name'],
];
$this->db->where('email', $array['email']);
$this->db->update('user', $updateData);