public static RelDataType convert(UnionTypeInfo unionType, RelDataTypeFactory dtFactory) {
    RelDataTypeFactory.Builder b = dtFactory.builder();
    for (TypeInfo ti : unionType.getAllUnionObjectTypeInfos()) {
      b.add(UNION_FIELD_PREFIX + b.getFieldCount(), convert(ti, dtFactory));
    }
    return b.build();
  }
******************** Convert Hive Types To Calcite Types **********************
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/translator/TypeConverter.java