Which product ids have received complaints?
select distinct product_id from complaints
What are the names of those products?
select distinct t1.product_name from products as t1 join complaints as t2 on t1.product_id = t2.product_id
Speaking of those names, count the number of complaints about them.
select t1.product_name, count(*) from products as t1 join complaints as t2 on t1.product_id = t2.product_id group by t1.product_name