question: public MergeJoinPlan ( Plan p1 , Plan p2 , String fldName1 , String fldName2 , Transaction tx ) { this . fldName1 = fldName1 ; List < String > sortlist1 = Arrays . asList ( fldName1 ) ; this . sp1 = new SortPlan ( p1 , sortlist1 , tx ) ; this . fldName2 = fldName2 ; List < String > sortlist2 = Arrays . asList ( fldName2 ) ; this . sp2 = new SortPlan ( p2 , sortlist2 , tx ) ; schema . addAll ( p1 . schema ( ) ) ; schema . addAll ( p2 . schema ( ) ) ; hist = joinHistogram ( p1 . histogram ( ) , p2 . histogram ( ) , fldName1 , fldName2 ) ; }
target:  Creates a mergejoin plan for the two specified queries. The RHS must be materialized after it is sorted, in order to deal with possible duplicates.