code: func (rev *Revocation) Select(tx *sql.Tx) error {
  	row := tx.QueryRow(`SELECT revoked_at, mechanism, reason FROM revocations WHERE ski=?`, rev.SKI)
  	err := row.Scan(&rev.RevokedAt, &rev.Mechanism, &rev.Reason)
  	if err != nil {
  		return err
  	}
  
  	return nil
  }
docs: // Select requires the SKI field to be filled in. Note that only one
  // revocation per SKI should exist.