Determine if CodeIgniter update query successfully affected any rows

How do I tell when a MySQL UPDATE was successful versus actually updated data?

Example:

TABLE
id    city_name
1     Union
2     Marthasville

If I run the following:

$data = array('city_name', 'Marthasville');

//update record 2 from Marthasville to the same thing, Marthasville. 
$this->db->where('id', 2);
$this->db->update('table', $data);

if($this->db->affected_rows() > 0)
{
    //I need it to return TRUE when the MySQL was successful even if nothing was actually updated.
    return TRUE;
}else{
    return FALSE;
}

This will return TRUE every time the UPDATE statement is successful, but FALSE when no rows were actually updated.

I need it to return TRUE every time the UPDATE statement was successfully executed even if it doesn't actually change any records.