@Override
  public Object getStructFieldData(Object data, StructField fieldRef) {
    return baseOI.getStructFieldData(data, fieldRef);
  }
Create a new Object Inspector based on a base object inspector and the subset of
columns will be inspected (from startCol to startCol+numCols).
@param baseOI
@param startCol
@param numCols
serde/src/java/org/apache/hadoop/hive/serde2/objectinspector/SubStructObjectInspector.java