public static JoinPredicateInfo constructJoinPredicateInfo(HiveMultiJoin mj, RexNode predicate) throws CalciteSemanticException {
      final List<RelDataTypeField> systemFieldList = ImmutableList.of();
      return constructJoinPredicateInfo(mj.getInputs(), systemFieldList, predicate);
    }
NOTE: Join Schema = left Schema + (right Schema offset by
left.fieldcount). Hence its ok to return projections from left in child
schema.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/HiveCalciteUtil.java