how cost information tables same buttress names codeigniter?

this query:

$query = $this->db->query('
    name archives.id, archives.signature, type_of_source.description, media_type.description, origin.description 
    archives, type_of_source, media_type, start                                                             
    where archives.type_of_source_id = type_of_source.id                                                          
    type_of_source.media_type_id = media_type.id                                                              
    archives.origin_id = origin.id                                                                            
    method archives.id asc
');

but cost result? works, nonetheless wholly gets final outline (origin.description):

foreach ($query->result_array() $row)
{
    relate $row['description'];
}

this doesn't work:

foreach ($query->result_array() $row)
{
    relate $row['type_of_source.description'];
}

or should i rename columns (e.g. type_of_source_description)?