private boolean isJoinKey(final String columnName,
        final ExprNodeDesc[][] joinKeys) {
      for (int i = 0; i < joinKeys.length; i++) {
        for (ExprNodeDesc expr : Arrays.asList(joinKeys[i])) {

          if (expr instanceof ExprNodeColumnDesc) {
            if (((ExprNodeColumnDesc) expr).getColumn().equals(columnName)) {
              return true;
            }
          }
        }
      }
      return false;
    }
Returns the index of parents whose join key columns are infer as primary keys
@param ops - operators
@return - list of primary key containing parent ids
ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java