SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function concat (children 1)
     ExpressionList (children 2)
      Literal NULL
      Function materialize (children 1)
       ExpressionList (children 1)
        Function CAST (children 1)
         ExpressionList (children 2)
          Literal NULL
          Literal \'Nullable(UInt64)\'