실험 환경

사용할 테이블

select * from SH.sales;

완성도

SQL 스크립트

View 사용

create view sales_cnt_view
as select CUST_ID cid, count(TIME_ID) as cnt_tid, TIME_ID tid
   from SH.SALES
   group by CUST_ID, TIME_ID;

select * from sales_cnt_view;

JOIN 이용

select s1.cid 顧客ID, s1.max_cnt_tid 顧客の購入商品種類の最大値, s2.tid 日付
from (select cid, MAX(cnt_tid) as max_cnt_tid
        from sales_cnt_view
        group by cid) s1
        join sales_cnt_view s2 on s1.cid = s2.cid and s1.max_cnt_tid = s2.cnt_tid
order by s1.cid;