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changes.mady.by.user Pengcheng Xiong

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Comment: document use of column aliases for hard-coded fields (thanks, Philippe Kernévez and Xuefu Zhang)

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Code Block
SELECT key FROM src
UNION
SELECT key FROM src1 
ORDER BY key LIMIT 10

When a specific column value is given in one or more SELECT statements (but not in all of them), the UNION may fail with an error message such as "FAILED: SemanticException 4:47 Schema of both sides of union should match." Column aliases should be used for such values, for example:

Code Block
languagetext
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
Info
titleVersion information

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.)

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