code: @Override
  	public void beforeFirst() {
  		currentScan = null;
  		s1.beforeFirst();
  		hasMore1 = s1.next();
  		if (s2 != null) {
  			s2.beforeFirst();
  			hasMore2 = s2.next();
  		}
  	}
docs: Positions the scan before the first record in sorted order. Internally,
  it moves to the first record of each underlying scan. The variable
  currentScan is set to null, indicating that there is no current scan.
  
  @see Scan#beforeFirst()