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INSERT OVERWRITE TABLE target_table
  SELECT name, id, category FROM source_table_1
  UNION ALL
  SELECT name, id, "Category159" as category FROM source_table_2

In Hive 0.12.0 and earlier releases, unions can only be used within a subquery such as "SELECT * FROM (select_statement UNION ALL select_statement UNION ALL ...) unionResult".

As of Hive 0.13.0, unions can also be used in a top-level query: "select_statement UNION ALL select_statement UNION ALL ...". (See HIVE-6189.)

Before Hive 1.2.0, only UNION ALL (bag union) is supported. UNION (or UNION DISTINCT) is supported since Hive 1.2.0. (See HIVE-9039.)