task.sql

1)
select users.first_name, users.last_name, users.email, count(orders.orders_id) as order_number
from [DZ1.users] users
left join [DZ1.orders] orders
on orders.user_id = users.id
group by orders.user_id, users.first_name, users.last_name, users.email
order by order_number desc
limit 5

2)
select users.country, sum(orders.order_sum) as total_sum 
from `DZ1.users` users 
left join `DZ1.orders` orders 
on orders.user_id = users.id
where users.country = 'Russia' or users.country = 'Brazil'
group by users.country 
order by total_sum desc
limit 1

3)
select count(users.email) as no_data 
from `DZ1.users` users 
left join `DZ1.orders` orders 
on users.id = orders.orders_id 
where orders.user_id is null

4)
select count(*) as no_user_data 
from  `DZ1.users` users 
right join `DZ1.orders` orders 
on users.id = orders.orders_id 
where users.id is null