code: func (b *builtinAtan2ArgsSig) evalReal(row chunk.Row) (float64, bool, error) {
  	val1, isNull, err := b.args[0].EvalReal(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  
  	val2, isNull, err := b.args[1].EvalReal(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  
  	return math.Atan2(val1, val2), false, nil
  }
docs: // evalReal evals a builtinAtan1ArgSig, corresponding to atan(y, x).
  // See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_atan