private Map<ExprNodeDesc, String> searchForEqualities(
            Operator<?> operator, Set<ExprNodeColumnDesc> exprNodeDescSet) {
      if (exprNodeDescSet.isEmpty()) {
        return Collections.emptyMap();
      }

      if (operator instanceof CommonJoinOperator) {
        return searchForEqualitiesInJoin((CommonJoinOperator<?>)operator, exprNodeDescSet);
      } else {
        return searchForEqualitiesDefault(operator, exprNodeDescSet);
      }
    }
Dispatcher method for column equality search traversal.

@param operator root of subtree to traverse
@param exprNodeDescSet set of columns search equal columns for
@return Map of equal columns: key column coming from the passed exprNodeDescSet, value the name of equal input
column of current operator.
ql/src/java/org/apache/hadoop/hive/ql/ppd/OpProcFactory.java