E-MapReduce:UNION ALL statement

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.

select_statement
UNION ALL
select_statement;

SELECT
    a,
    sum(b),
FROM 
    (SELECT * from tb_1
    UNION ALL
    SELECT * from tb_2
    )t
 GROUP BY a;