SELECT pu.user_id, pu.point, a.avg_likes from point_users pu

inner join(

SELECT user_id, round(avg(likes),1) as avg_likes from checkins c

group by user_id

) a on pu.user_id = a.user_id

SELECT * from

(

SELECT course_id, COUNT(DISTINCT(user_id)) as cnt_checkins from checkins

group by course_id

)a

inner JOIN

(

SELECT course_id , count(*) as cnt_total from orders

group by course_id

) b on a.course_id = b.course_id

두 방식의 join이 있는데 밑에 거를 위에 것처럼 join을 하니까 에러가 납니다. 차이가 무엇인가요?

에러가 나는 방식은 밑에 있습니다.

SELECT c.course_id, COUNT(DISTINCT (c.user_id)) from checkins c

group by c.course_id

inner join

(

select o.course_id, count(*) from orders o

group by o.course_id

) a on c.course_id = a.course_id