public int getOutputValueColumnCount() {
    if (outputValueColumnCount == null) {
      HashSet<String> columnNameSet = new HashSet<>();
      for (ColumnHeader columnHeader : columnHeaders) {
        columnNameSet.add(columnHeader.getColumnName());
      }
      outputValueColumnCount = columnNameSet.size();
    }
    return outputValueColumnCount;
  }
The header of query result dataset.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/common/header/DatasetHeader.java