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Hive SQL - Union data with UNION ALL and UNION DISTINCT

event 2022-07-23 visibility 2,611 comment 0 insights toc
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Like other data warehouse software, Hive provides built-in clauses to union data - UNION ALL and UNION DISTINCT (UNION). UNION ALL will include all records in both left and right tables while UNION will only return distinct records only. You can mix these two unions in one query but the UNION will overwrites any UNION ALL to its left.

Syntax

select_statement UNION [ALL | DISTINCT] select_statement [UNION [ALL | DISTINCT] select_statement) *

Code snippet

The following code snippet provides one example of using 

SELECT acct, txn_date, amount from transactions UNION ALL select 104, DATE'2022-07-23', 200;

Sample result:

101     2021-01-01      10.01
101     2021-01-01      102.01
102     2021-01-01      93.00
103     2021-01-02      913.10
102     2021-01-02      913.10
101     2021-01-03      900.56
104     2022-07-23      200.00

The following is another example using UNION DISTINCT.

SELECT acct, txn_date from transactions UNION DISTINCT select 104, DATE'2022-07-23';

The result will remove duplicated records:

101     2021-01-01
101     2021-01-03
102     2021-01-01
102     2021-01-02
103     2021-01-02
104     2022-07-23

The above sample table is from Hive SQL - Analytics with GROUP BY and GROUPING SETS, Cubes, Rollups.

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