public void addNaturalJoinColumn(Column c){
  if (naturalJoinColumns == null) {
    naturalJoinColumns=New.arrayList();
  }
  naturalJoinColumns.add(c);
}

public void addNaturalJoinColumn ( Column c ) { if ( naturalJoinColumns == null ) { naturalJoinColumns = New . arrayList ( ) ; } naturalJoinColumns . add ( c ) ; }
add a column to the natural join key column list .
