create table Product_1083(product_id int, product_name varchar(10), unit_price double);

insert into Product_1083(product_id, product_name, unit_price) values(1, 'S8', 1000), (2, 'G4', 800), (3, 'iphone', 1400);

create table Sales_1083(seller_id int, product_id int, buyer_id int, sale_date date, quantity int, price double);

insert into Sales_1083(seller_id, product_id, buyer_id, sale_date, quantity, price) values(1, 1, 1, '2019-01-21', 2, 2000), (1, 2, 2, '2019-02-17', 1, 800), (2, 1, 3, '2019-06-02', 1, 800), (3, 3, 3, '2019-05-13', 2, 2800);

with cte as (select s.*, p.product_name

from Product_1083 p join Sales_1083 s

on p.product_id=s.product_id)

select distinct buyer_id from cte where product_name='S8'

and buyer_id not in (select distinct buyer_id from cte where product_name='iphone');