select user_id , name, email from users where user_id in ( select user_id from orders where payment_method = 'kakaopay' ) select c.checkin_id , c2.title , c.user_id , c.likes, ( select round(avg(likes),1) from checkins c where course_id = c.course_id ) as course_avg from checkins c inner join courses c2 on c.course_id = c2.course_id select pu.user_id, pu.point, (case when pu.point > 10000 then '..

Left join: 왼쪽에 붙이는 것. 해당되는 값이 없는 경우에는 Null로 표기됨 Inner join: 교집합이 나온다. 같이 공유하는 리스트를 중심으로 붙여짐. select * from enrolleds e inner join users u on e.user_id = u.user_id Immerge by course_id, count couse_id and title, and show the head of them. select c1.course_id, c2.title, count(*) as cnt from checkins c1 inner join courses c2 on c1.course_id = c2.course_id group by c1.course_id select pu.user_id , u..

select payment_method, count(*) from orders group by payment_method kakaopay 56 CARD 218 TAXBILL 4 MONEY 8 select payment_method, count(*) from orders where course_title = '앱개발 종합반' group by payment_method kakaopay 34 CARD 111 MONEY 5 TAXBILL 3 select name, count(*) from users where email like "%gmail.com" group by name 신** 7 이** 29 강** 5 김** 32 심** 3 남** 5 문** 1 손** 1 윤** 3 안** 1 권** 4 박** 7 유*..