code: func (b *builtinIsIPv6Sig) evalInt(row chunk.Row) (int64, bool, error) {
  	val, isNull, err := b.args[0].EvalString(b.ctx, row)
  	if err != nil || isNull {
  		return 0, err != nil, err
  	}
  	ip := net.ParseIP(val)
  	if ip != nil && !isIPv4(val) {
  		return 1, false, nil
  	}
  	return 0, false, nil
  }
docs: // evalInt evals a builtinIsIPv6Sig.
  // See https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html#function_is-ipv6