code: private DataContainer fetch(String tableAlias, IndexBooleanExpression condition, Map<String, String> tableAliases) {
          String tableName = tableAliases.get(tableAlias);
          Set<String> ids = getIdsFromIndex(tableName, tableAlias, condition);
          return fetchContainer(tableName, tableAlias, ids);
      }
docs: planner should guarantee that.