code: func (ssa *SQLStorageAuthority) getFQDNSetsBySerials(
  	db dbSelector,
  	serials []string,
  ) ([]setHash, error) {
  	var fqdnSets []setHash
  
  	// It is unexpected that this function would be called with no serials
  	if len(serials) == 0 {
  		err := fmt.Errorf("getFQDNSetsBySerials called with no serials")
  		ssa.log.AuditErr(err.Error())
  		return nil, err
  	}
  
  	qmarks := make([]string, len(serials))
  	params := make([]interface{}, len(serials))
  	for i, serial := range serials {
  		params[i] = serial
  		qmarks[i] = "?"
  	}
  	query := "SELECT setHash FROM fqdnSets " +
  		"WHERE serial IN (" + strings.Join(qmarks, ",") + ")"
  	_, err := db.Select(
  		&fqdnSets,
  		query,
  		params...)
  
  	if err != nil {
  		return nil, err
  	}
  
  	// The serials existed when we found them in issuedNames, they should continue
  	// to exist here. Otherwise an internal consistency violation occured and
  	// needs to be audit logged
  	if err == sql.ErrNoRows {
  		err := fmt.Errorf("getFQDNSetsBySerials returned no rows - internal consistency violation")
  		ssa.log.AuditErr(err.Error())
  		return nil, err
  	}
  	return fqdnSets, nil
  }
docs: // getFQDNSetsBySerials finds the setHashes corresponding to a set of
  // certificate serials. These serials can be used to check whether any
  // certificates have been issued for the same set of names previously.