private List<String> getSingleValuedColumnNames(Set<PartitionFieldNode> roots) {
    List<String> columnNames = new ArrayList<>();
    int fieldIndex = 0;
    for (PartitionFieldNode node : roots) {
      fieldIndex = getSingleValuedColumnName(node, fieldIndex, columnNames);
    }
    return columnNames;
  }
Given a list of partition ids, returns the List of partially filled partitions based on the
projection list used to instantiate this PartitionProjectionEvaluator
@param partitionIds List of partition ids corresponding to the Partitions objects which are requested
@return Partitions where each partition has only the projected fields set
@throws MetaException
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/PartitionProjectionEvaluator.java