code: func (b *builtinStrcmpSig) evalInt(row chunk.Row) (int64, bool, error) {
  	var (
  		left, right string
  		isNull      bool
  		err         error
  	)
  
  	left, isNull, err = b.args[0].EvalString(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  	right, isNull, err = b.args[1].EvalString(b.ctx, row)
  	if isNull || err != nil {
  		return 0, isNull, err
  	}
  	res := types.CompareString(left, right)
  	return int64(res), false, nil
  }
docs: // evalInt evals a builtinStrcmpSig.
  // See https://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html