CREATE TABLE products (product_details VARCHAR2, product_id VARCHAR2)
CREATE TABLE order_items (product_id VARCHAR2)

Which product has been ordered most number of times?
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
SELECT "t2"."product_details" FROM "order_items" "t1" JOIN "products" "t2" ON "t1"."product_id" = "t2"."product_id" GROUP BY "t1"."product_id" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY