public RelNode convertSelect(SqlSelect select,boolean top){
  final SqlValidatorScope selectScope=validator.getWhereScope(select);
  final Blackboard bb=createBlackboard(selectScope,null,top);
  convertSelectImpl(bb,select);
  return bb.root;
}

public RelNode convertSelect ( SqlSelect select , boolean top ) { final SqlValidatorScope selectScope = validator . getWhereScope ( select ) ; final Blackboard bb = createBlackboard ( selectScope , null , top ) ; convertSelectImpl ( bb , select ) ; return bb . root ; }
converts a select statement ' s parse tree into a relational expression .
