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create table sales( customer_id varchar(1) not null, order_date date, product_id int not null, qty int ); create table menu( product_id int, product_name varchar(10) not null, price int default 0, ); create table member( customer_id varchar(1) not null, join_date date ); insert into sales(customer_id, order_date, product_id, qty) values ('A','1/1/2021',1, 2), ('A','1/1/2021',2, 2), ('A','1/7/2021',2, 2), ('A','1/10/2021',3, 1), ('A','1/11/2021',3, 1), ('A','1/11/2021',3, 3), ('B','1/1/2021',2, 2), ('B','1/2/2021',2, 1), ('B','1/4/2021',1, 3), ('B','1/11/2021',1, 2), ('B','1/16/2021',3, 3), ('B','2/1/2021',3, 3), ('C','1/1/2021',3, 2), ('C','1/1/2021',3, 1), ('C','1/7/2021',3, 1) ; insert into menu(product_id, product_name, price) values (1, 'sushi roll', 10), (2, 'curry', 15), (3, 'ramen', 12), (4, 'edamame', 7), (5, 'onion ring', 5), (6, 'sashimi', 22) ; insert into member(customer_id, join_date) values ('A', '2021/1/7'); insert into member(customer_id, join_date) values ('B', '2021/1/9'); insert into member(customer_id, join_date) values ('C', '2021/1/31'); select * from member; SELECT product_id FROM Menu m FULL OUTER JOIN Sales s ON m.product_id = s.product_id WHERE NOT EXISTS ( SELECT s.product_id FROM Sales s );