|UNIONTYPE support is incomplete|
The UNIONTYPE datatype was introduced in Hive 0.7.0 (HIVE-537). See HIVE-2390 for planned improvements., but full support for this type in Hive remains incomplete. Queries that reference UNIONTYPE fields in JOIN (HIVE-2508), WHERE, and GROUP BY clauses will fail, and Hive does not define syntax to extract the tag or value fields of a UNIONTYPE. This means that UNIONTYPEs are effectively look-at-only.
Union types can at any one point hold exactly one of their specified data types. You can create an instance of this type using the