code: func builtinStrcmp(args []types.Datum, _ context.Context) (d types.Datum, err error) {
  	if args[0].IsNull() || args[1].IsNull() {
  		return d, nil
  	}
  	left, err := args[0].ToString()
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	right, err := args[1].ToString()
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	res := types.CompareString(left, right)
  	d.SetInt64(int64(res))
  	return d, nil
  }
docs: // See https://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html