code: func (cr *CertificateRelease) Select(tx *sql.Tx) error {
  	var count int
  	query := fmt.Sprintf("SELECT count(*) FROM %ss WHERE ski=? AND serial=? AND release=?", cr.Release.table())
  	row := tx.QueryRow(query, cr.Certificate.SKI, cr.Certificate.Serial, cr.Release.Version)
  	err := row.Scan(&count)
  	if err == nil && count == 0 {
  		return sql.ErrNoRows
  	}
  	return err
  }
docs: // Select requires the Certificate field to have the SKI and Serial
  // filled in, and the Release field to have the Version field filled
  // in.