A UNION ALL statement is used to combine two data streams. The fields of the two data streams must be the same in terms of the field type and sequence.

Syntax

select_statement
UNION ALL
select_statement;
Note Realtime Compute also supports the UNION function. UNION ALL allows duplicate values, whereas UNION does not. At the underlying layer of Realtime Compute, UNION is implemented as a combination of UNION ALL and DISTINCT. Due to its low execution efficiency, we recommend that you do not use UNION.

Examples

  • Test data

    test_source_union1:

    a (VARCHAR) b (BIGINT) c (BIGINT)
    test1 1 10

    test_source_union2:

    a (VARCHAR) b (BIGINT) c (BIGINT)
    test1 1 10
    test2 2 20

    test_source_union3:

    a (VARCHAR) b (BIGINT) c (BIGINT)
    test1 1 10
    test2 2 20
    test1 1 10
  • Test statements
    SELECT
    a,
    sum(b),
    sum(c)
FROM 
    (SELECT * from test_source_union1
    UNION ALL
    SELECT * from test_source_union2
    UNION ALL
    SELECT * from test_source_union3
    )t
 GROUP BY a;
  • Test result
    d (VARCHAR) e (BIGINT) f (BIGINT)
    test1 1 10
    test2 2 20
    test1 2 20
    test1 3 30
    test2 4 40
    test1 4 40