public SelectPlan(Plan p,Predicate pred){
  this.p=p;
  this.pred=pred;
  hist=predHistogram(p.histogram(),pred);
}

public SelectPlan ( Plan p , Predicate pred ) { this . p = p ; this . pred = pred ; hist = predHistogram ( p . histogram ( ) , pred ) ; }
creates a new select node in the query tree , having the specified subquery and predicate .
