function build_db_join_relation($related_table, $unique_name, $related_primary_key, $field_name)
 {
     if ($this->subdriver == 'pgsql') {
         $this->db->join($this->protect_identifiers($related_table) . ' as ' . $this->protect_identifiers($unique_name), 'cast(' . $this->protect_identifiers($unique_name . '.' . $related_primary_key) . ' as character varying) = cast(' . $this->protect_identifiers($this->table_name . '.' . $field_name) . ' as character varying)', 'left', FALSE);
     } else {
         parent::build_db_join_relation($related_table, $unique_name, $related_primary_key, $field_name);
     }
 }