1. Left join
select * from a
left join b
on a.id = b.id
select * from a
right join b
on a.id = b.id
select * from a
inner join b
on a.id = b.id
테이블간 서로 연결되는 칼럼만 출력
SQL에서는 default값으로 join을 사용하면 inner join 연산이 수행된다.
select * from a
full outer join b
on a.id = b.id
합집합
https://lcs1245.tistory.com/entry/SQL-JOIN-INNER-JOIN-OUTER-JOIN-LEFT-JOIN-RIGHT-JOIN-SELF-JOIN