
SELECT total_bill,tip,sex,smoker,day,time,size
FROM (SELECT * FROM tips) a
JOIN (SELECT avg(total_bill) avg FROM tips) b
WHERE total_bill > b.avg
SELECT *
FROM tips
WHERE total_bill > (SELECT avg(total_bill) FROM tips)
where 절에서 서브쿼리로 조건 적용하면 더 쉽게 풀이 가능하다.