anchor.diff:    int _rowsAffected;
     
     List<String> _columnNames;
  -  Map<String, int> _columnIndex;
  +  Map<Symbol, int> _columnIndex;
     
     _Query(this.sql);
     
  
positive.code:   }
    
    // Map column name to column index
    final Map<String, int> _index;
    final List<String> _columnNames;
    final List _columnValues;
    
  
negative.code:     
      _columnNames = _columns.map((c) => c.name).toList();
      
      var ident = new RegExp(r'^[a-zA-Z][a-zA-Z0-9_]*$');
      _columnIndex = new Map<Symbol, int>();
      for (var i = 0; i < _columnNames.length; i++) {
        var name = _columnNames[i];
        if (ident.hasMatch(name))
          _columnIndex[new Symbol(name)] = i;
      }
    }
    
  