## 1661. Average Time of Process per Machine

Question:

Solution:

``````select
a.machine_id,
round(sum(a.duration)/count(distinct a.process_id),3) as processing_time
from(
select
s.machine_id,
s.process_id,
(e.end_time- s.start_time) as duration
from(
select
machine_id,
process_id,
timestamp as start_time
from Activity
where activity_type = 'start'
) s
left join (
select
machine_id,
process_id,
timestamp as end_time
from Activity
where activity_type = 'end'
) e
on (s.machine_id = e.machine_id and s.process_id = e.process_id )
) a
group by 1
order by 1``````

## 1667. Fix Names in a Table

Question:

Solution:

``````select
user_id,
concat(upper(mid(name,1,1)),lower(mid(name,2))) as name
from Users
order by 1``````

## 1677. Product’s Worth Over Invoices

Question:

Solution:

``````select p.name,
ifnull(sum(i.rest),0) as rest,
ifnull(sum(i.paid),0) as paid,
ifnull(sum(i.canceled),0) as canceled,
ifnull(sum(i.refunded),0) as refunded
from Product p
inner join Invoice i
on p.product_id = i.product_id
group by 1
order by 1``````