code: func ExecuteErrorToLabel(err error) string {
  	err = errors.Cause(err)
  	switch x := err.(type) {
  	case *terror.Error:
  		return x.Class().String() + ":" + strconv.Itoa(int(x.Code()))
  	default:
  		return "unknown"
  	}
  }
docs: // ExecuteErrorToLabel converts an execute error to label.