  const char *type_name()
  {
    return type == COLUMN ? "COLUMN" :
           type == CHECK_CONSTRAINT ? "CONSTRAINT" :
           type == KEY ? "INDEX" : "FOREIGN KEY";
  }
  const char *type_name()
  {
    return type == COLUMN ? "COLUMN" :
           type == CHECK_CONSTRAINT ? "CONSTRAINT" :
           type == KEY ? "INDEX" : "FOREIGN KEY";
  }