code: func (b *builtinAbsIntSig) evalInt(row chunk.Row) (int64, bool, error) {
  	val, isNull, err := b.args[0].EvalInt(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  	if val >= 0 {
  		return val, false, nil
  	}
  	if val == math.MinInt64 {
  		return 0, false, types.ErrOverflow.GenWithStackByArgs("BIGINT", fmt.Sprintf("abs(%d)", val))
  	}
  	return -val, false, nil
  }
docs: // evalInt evals ABS(value).
  // See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_abs