List<ExprNodeDesc> colList = new ArrayList<ExprNodeDesc>();
ExprNodeColumnDesc colDesc1 = new ExprNodeColumnDesc(Long.class, "a", "table", false);
ExprNodeColumnDesc colDesc2 = new ExprNodeColumnDesc(Long.class, "b", "table", false);
ExprNodeColumnDesc colDesc3 = new ExprNodeColumnDesc(Long.class, "c", "table", false);
ExprNodeGenericFuncDesc plusDesc = new ExprNodeGenericFuncDesc();
GenericUDF gudf = new GenericUDFOPPlus();
plusDesc.setGenericUDF(gudf);
List<ExprNodeDesc> children = new ArrayList<ExprNodeDesc>();
children.add(colDesc1);
children.add(colDesc2);