AlterQuery  z (children 2)
 ExpressionList (children 1)
  AlterCommand ADD_PROJECTION (children 1)
   Projection (children 1)
    ProjectionSelectQuery (children 2)
     ExpressionList (children 2)
      Identifier id
      Function sum (children 1)
       ExpressionList (children 1)
        Identifier c
     ExpressionList (children 1)
      Identifier id
 Identifier z