code: func (b *builtinFoundRowsSig) evalInt(row chunk.Row) (int64, bool, error) {
  	data := b.ctx.GetSessionVars()
  	if data == nil {
  		return 0, true, errors.Errorf("Missing session variable when eval builtin")
  	}
  	return int64(data.LastFoundRows), false, nil
  }
docs: // evalInt evals a builtinFoundRowsSig.
  // See https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_found-rows
  // TODO: SQL_CALC_FOUND_ROWS and LIMIT not support for now, We will finish in another PR.