id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE plz4 ALL NULL NULL NULL NULL 5321 Using where; Using temporary; Using filesort 1 SIMPLE steuern ref gemeindeID gemeindeID 5 cluster.plz4.gemeindeID 1 Using where 1 SIMPLE gemeinde eq_ref PRIMARY PRIMARY 4 cluster.steuern.gemeindeID 1 Using where 1 SIMPLE bezirk eq_ref PRIMARY PRIMARY 4 cluster.gemeinde.bezirkID 1 1 SIMPLE steuern_kanton eq_ref PRIMARY PRIMARY 4 cluster.bezirk.kantonID 1