[leetcode] 1148. Article Views I

테이블 생성 코드

Create table If Not Exists Views (article_id int, author_id int, viewer_id int, view_date date)

Truncate table Views

insert into Views (article_id, author_id, viewer_id, view_date) values ('1', '3', '5', '2019-08-01')

insert into Views (article_id, author_id, viewer_id, view_date) values ('1', '3', '6', '2019-08-02')

insert into Views (article_id, author_id, viewer_id, view_date) values ('2', '7', '7', '2019-08-01')

insert into Views (article_id, author_id, viewer_id, view_date) values ('2', '7', '6', '2019-08-02')

insert into Views (article_id, author_id, viewer_id, view_date) values ('4', '7', '1', '2019-07-22')

insert into Views (article_id, author_id, viewer_id, view_date) values ('3', '4', '4', '2019-07-21')

insert into Views (article_id, author_id, viewer_id, view_date) values ('3', '4', '4', '2019-07-21')

 

문제 

 

해결 코드

SELECT DISTINCT(author_id) AS id

FROM Views

WHERE author_id = viewer_id

ORDER BY author_id;

 

풀이

글쓴이가 자신이 쓴글을 자신이 한번이라도 봐야하므로

author_id = viewer_id 인조건을 where 절에 넣는다

그리고 중복값이 생기면 한번만 출력하기 위해

select 절에 distinct를 사용하여

DISTINCT(author_id)  게 적고

출력되는 컬럼명을 바꾸기 위해

DISTINCT(author_id) AS id 라고 적는다.