TableDesc keyTableDesc = PlanUtils.getReduceKeyTableDesc(PlanUtils
.getFieldSchemasFromColumnList(keyCols, "mapjoinkey"), keyOrder.toString());
mapJoinOp.getConf().setKeyTableDesc(keyTableDesc);
// let the dummy op be the parent of mapjoin op
mapJoinOp.replaceParent(parentRS, dummyOp);
List<Operator<? extends OperatorDesc>> dummyChildren =
new ArrayList<Operator<? extends OperatorDesc>>();
dummyChildren.add(mapJoinOp);
dummyOp.setChildOperators(dummyChildren);
dummyOperators.add(dummyOp);