THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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SELECT key FROM src UNION SELECT key FROM src1 ORDER BY key LIMIT 10 |
Column Aliases for
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Schema Matching
UNION ALL expects expects the same schema on both sides of the expression list. As a result, the following query may fail with an error message such as "FAILED: SemanticException 4:47 Schema of both sides of union should match."
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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 |
Column Type Conversion
Before HIVE-14251 in release 2.2.0, Hive tries to perform implicit conversion across Hive type groups. With the change of HIVE-14251, Hive will only perform implicit conversion within each type group including string group, number group or date group, not across groups. In order to union the types from different groups such as a string type and a date type, an explicit cast from string to date or from date to string is needed in the query.
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SELECT name, id, cast('2001-01-01' as date) d FROM source_table_1 UNION ALL SELECT name, id, hiredate as d FROM source_table_2 |
Version Information
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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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