code: func (pk PrimaryKey) String() string {
  	var b bytes.Buffer
  	b.WriteByte('(')
  	b.WriteString(formatPartitionKeys(pk.PartitionKeys))
  	if pk.ClusteringKeys != nil && len(pk.ClusteringKeys) > 0 {
  		b.WriteString(", ")
  		b.WriteString(formatClusteringKeys(pk.ClusteringKeys))
  	}
  	b.WriteByte(')')
  	return b.String()
  }
docs: // String method produces the following output:
  // for multiple partition keys: ((partition-key, ...), clustering-key ASC/DESC, ...)
  // for one partition key: (partition-key, clustering-key ASC/DESC, ...)