/*
Задача 1:

Для каждой категории показать 2 строки:
- Самый дорогой товар с email'ом
- Самый дорогой товар без email'а
*/
with with_mail as (
select category, name, price, email_support
from (
select category, name, price, email_support,
row_number() over (partition by category order by price desc) as rn
from products_extended 
where email_support is not null
) t
where rn = 1
),
without_mail as (
select category, name, price, email_support
from (
select category, name, price, email_support,
row_number() over (partition by category order by price desc) as rn
from products_extended
where email_support is null
) t
where rn = 1 
)

select * from with_mail
union all
select * from without_mail
order by category;

/*
Задача 2:

Для каждого товара показать:

- `name` — название товара
- `category` — категория товара
- `price` — цена текущего товара
- `next_price` — цена следующего товара внутри той же категории, упорядоченного по цене
- `diff` — разница между ценой текущего товара и ценой следующего товара 
(`price - next_price`)
*/

select name, category, price, lead(price) over(partition by category order by price) as next_price, 
price - lead(price) over(partition by category order by price) as diff
from products_extended;

/*
Задача 3:

Показать `category`, `name`, `price`, `cumulative_sales`

Где `cumulative_sales` — это сумма `price` **внутри категории** по мере возрастания цены
*/

select category, name, price, 
sum(price) over (partition by category order by price) as cumulative_sales
from products_extended;

/*
Задача 4:

Вывести `category`, `name`, `price`, `avg_price`, `is_above_avg`

Где `avg_price` — средняя цена по категории

`is_above_avg = true`, если `price > avg_price`

*/

select  category, name, price, 
round(avg(price) over (partition by category), 1) as avg_price,
price > avg(price) over (partition by category) as is_above_avg
from products_extended;