먼저 Dataset 코드입니다.DROP TABLE IF EXISTS purchase_log_with_coupon;CREATE TABLE purchase_log_with_coupon ( purchase_id varchar(255) , amount integer , coupon integer);INSERT INTO purchase_log_with_couponVALUES ('10001', 3280, NULL) , ('10002', 4650, 500) , ('10003', 3870, NULL) , ('10004', 2670, 400) , ('10005', 3219, NULL) , ('10006', 9853, 200); 결손값 처리(COALESCE)결손값(null)값 처리..
