code: func (ssa *SQLStorageAuthority) CountFQDNSets(ctx context.Context, window time.Duration, names []string) (int64, error) {
  	var count int64
  	err := ssa.dbMap.WithContext(ctx).SelectOne(
  		&count,
  		`SELECT COUNT(1) FROM fqdnSets
  		WHERE setHash = ?
  		AND issued > ?`,
  		hashNames(names),
  		ssa.clk.Now().Add(-window),
  	)
  	return count, err
  }
docs: // CountFQDNSets returns the number of sets with hash |setHash| within the window
  // |window|