[오라클(Oracle)] UNION, UNION ALL

UNION과 UNIONALL

UNION = 두테이블의 결합을 나타내며 중복되지 않은 값들을 반환

UNION ALL = 두테이블의 중복되는 값까지 반환

table_a

-------

1

2

3

table_b

-------

2

3

4

1) union

select column_1 from table_a 

union

select column_1 from table_b

-> 1, 2, 3, 4

2) union all

select * from column_1 from table_a

union all

select * from column_1 from table_b

-> 1,2,3,2,3,4