code: func (b *builtinUTCTimestampWithArgSig) evalTime(row chunk.Row) (types.Time, bool, error) {
  	num, isNull, err := b.args[0].EvalInt(b.ctx, row)
  	if err != nil {
  		return types.Time{}, true, err
  	}
  
  	if !isNull && num > int64(types.MaxFsp) {
  		return types.Time{}, true, errors.Errorf("Too-big precision %v specified for 'utc_timestamp'. Maximum is %v.", num, types.MaxFsp)
  	}
  	if !isNull && num < int64(types.MinFsp) {
  		return types.Time{}, true, errors.Errorf("Invalid negative %d specified, must in [0, 6].", num)
  	}
  
  	result, isNull, err := evalUTCTimestampWithFsp(b.ctx, int(num))
  	return result, isNull, err
  }
docs: // evalTime evals UTC_TIMESTAMP(fsp).
  // See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_utc-timestamp