private List<RexNode> toRexNodeList(RelNode srcRel) {
      return srcRel.getRowType().getFieldList().stream()
              .map(input -> new RexInputRef(input.getIndex(), input.getType()))
              .collect(Collectors.toList());
    }
Generate OB RelNode and input Select RelNode that should be used to
introduce top constraining Project. If Input select RelNode is not
present then don't introduce top constraining select.

@param qb
@param selPair
@param outermostOB
@return RelNode OB RelNode
@throws SemanticException
ql/src/java/org/apache/hadoop/hive/ql/parse/CalcitePlanner.java