code: func NamedExec(e Ext, query string, arg interface{}) (sql.Result, error) {
  	q, args, err := bindNamedMapper(BindType(e.DriverName()), query, arg, mapperFor(e))
  	if err != nil {
  		return nil, err
  	}
  	return e.Exec(q, args...)
  }
docs: // NamedExec uses BindStruct to get a query executable by the driver and
  // then runs Exec on the result.  Returns an error from the binding
  // or the query execution itself.