code: func (b *builtinLastInsertIDWithIDSig) evalInt(row chunk.Row) (res int64, isNull bool, err error) {
  	res, isNull, err = b.args[0].EvalInt(b.ctx, row)
  	if isNull || err != nil {
  		return res, isNull, err
  	}
  
  	b.ctx.GetSessionVars().SetLastInsertID(uint64(res))
  	return res, false, nil
  }
docs: // evalInt evals LAST_INSERT_ID(expr).
  // See https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_last-insert-id.