AlterQuery  add_materialized_column_after (children 2)
 ExpressionList (children 1)
  AlterCommand ADD_COLUMN (children 2)
   ColumnDeclaration y (children 2)
    DataType String
    Function toString (children 1)
     ExpressionList (children 1)
      Identifier x
   Identifier x
 Identifier add_materialized_column_after
