Сергей

using System;

namespace LastPositiveNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            int result = 0;
            int[] array = new int[10] { 1, 2, -5, 7, 9, -3, 4, 5, -7, -5 };

            foreach (var item in array)
                result = item > 0 ? item : result;

            if (result > 0)
                Console.WriteLine(result);
            else
                Console.WriteLine("Положительных чисел нет");
            Console.ReadLine();
        }
    }
}

with cat_max(cat_id, max_price) as 
(
	select category, MAX(price)
	from Product
	group by category
)

select c.name as 'Category', p.name as 'Product', cm.max_price as 'Max price'
from Product as p join cat_max as cm
	on p.price = cm.max_price
	and p.category = cm.cat_id
	join Category as c on c.id = cm.cat_id