SQL 3주차
3-2강
[Joint을 사용해서 Key값으로 두테이블 연결해보기]
select * from point_users
left join users
on point_users.user_id = users.user_id
[유저데이터로 Inner Join 이해해보기]
select * from users u
inner join point_users p
on u.user_id = p.user_id;
[과목별 오늘의 다짐 갯수 세어보기]
select co.title, count(co.title) as checkin_count from checkins ci
inner join courses co
on ci.course_id = co.course_id
group by co.title
[많은 포인트를 얻은 순서대로 유저 데이터 정렬해서 보기]
select * from point_users p
inner join users u
on p.user_id = u.user_id
order by p.point desc
[네이버 이메일 사용하는 유저의 성씨벌 주문건수 세어보기]
select u.name, count(u.name) as count_name from orders o
inner join users u
on o.user_id = u.user_id
where u.email like '%naver.com'
group by u.name
3-3강 퀴즈
1) 결제 수단 별 유저 포인트의 평균값 구해보기
select o.payment_method, round(AVG(p.point)) from point_users p
inner join orders o
on p.user_id = o.user_id
group by o.payment_method
2) 결제하고 시작하지 않은 유저들을 성씨별로 세어보기
select name, count(*) as cnt_name from enrolleds e
inner join users u
on e.user_id = u.user_id
where is_registered = 0
group by name
order by cnt_name desc
3) 과목 별로 시작하지 않은 유저들을 세어보기
select c.course_id, c.title, count(*) as cnt_notstart from courses c
inner join enrolleds e
on c.course_id = e.course_id
where is_registered = 0
group by c.course_id
4) 웹개발, 앱개발 종합반의 week 별 체크인 수를 세어보기
select c1.title, c2.week, count(*) as cnt from checkins c2
inner join courses c1 on c2.course_id = c1.course_id
group by c1.title c2.week
order by c1.title, c2.week
5) 연습4번에서, 8월 1일 이후에 구매한 고객들만 발라내기
select c1.title, c2.week, count(*) as cnt from courses c1
inner join checkins c2 on c1.course_id = c2.course_id
inner join orders o on c2.user_id = o.user_id
where o.created_at >= '2020-08-01'
group by c1.title, c2.week
order by c1.title, c2.week
3-5강
1) Left join에서 Null값을 제외하고 뽑기
select name, count(*) from users u
left join point_users pu on u.user_id = pu.user_id
where pu.point_user_id is not NULL group by name
2) 7월10일 ~ 7월19일에 가입한 고객 중, 포인트를 가진 고객의 숫자, 전체 숫자, 그리고 비율보기
select count(point_user_id) as pnt_user_cnt,
count(*) as tot_user_cnt,
round(count(point_user_id)/count(*),2) as ratio
from users u
left join point_users pu on u.user_id = pu.user_id
where u.created_at between '2020-07-10' and '2020-07-20'
3-6강
union all 문법
(
select '7월' as month, c.title, c2.week, count(*) as cnt from checkins c2
inner join courses c on c2.course_id = c.course_id
inner join orders o on o.user_id = c2.user_id
where o.created_at < '2020-08-01'
group by c2.course_id, c2.week
order by c2.course_id, c2.week
)
union all
(
select '8월' as month, c.title, c2.week, count(*) as cnt from checkins c2
inner join courses c on c2.course_id = c.course_id
inner join orders o on o.user_id = c2.user_id
where o.created_at > '2020-08-01'
group by c2.course_id, c2.week
order by c2.course_id, c2.week
)
