code: func NamedQuery(e Ext, query string, arg interface{}) (*Rows, error) {
  	q, args, err := bindNamedMapper(BindType(e.DriverName()), query, arg, mapperFor(e))
  	if err != nil {
  		return nil, err
  	}
  	return e.Queryx(q, args...)
  }
docs: // NamedQuery binds a named query and then runs Query on the result using the
  // provided Ext (sqlx.Tx, sqlx.Db).  It works with both structs and with
  // map[string]interface{} types.