@Override
  public void replaceTabAlias(String oldAlias, String newAlias) {
    super.replaceTabAlias(oldAlias, newAlias);
    ExprNodeDescUtils.replaceTabAlias(getConf().getColumnExprMap(), oldAlias, newAlias);
  }
Checks whether this select operator does something to the
input tuples.

@return if it is an identity select operator or not
ql/src/java/org/apache/hadoop/hive/ql/exec/SelectOperator.java