[Oracle] union, union all

union
    - select 결과를 합칠 수 있음
    - 합친 결과에서 중복되는 행을 제거
    - 컬럼의 개수가 같아야 하고, 각 컬럼의 데이터타입이 같아야 함
    
union all
    - union과 같지만 중복된 행을 제거하지 않음

 

주문 테이블 조회

select * from tb_order;

union

중복된 행 제거

select ord_userid, ord_regdate from tb_order
union 
select ord_userid, ord_regdate from tb_order where ord_price >= 1000000;

union all

중복된 행 제거 x

select ord_userid, ord_regdate from tb_order
union all
select ord_userid, ord_regdate from tb_order where ord_price >= 1000000;