Count the number of times each product is ordered.
select count(*) from order_items group by product_id
What is the most frequently ordered product?
select * from order_items group by product_id order by count(*) desc limit 1
Tell me the detail of the product.
select t2.product_details from order_items as t1 join products as t2 on t1.product_id = t2.product_id group by t1.product_id order by count(*) desc limit 1