mysql - How to divide two summed columns from two grouped by queries? -

i have following query:

select      date_format(created_at,'%y-%m-%d %h:00:00') date,      sum(quantity) total     request_items     group hour( created_at ) 

it generates report summing quantities hour. got this:

2017-04-01 00:00:00 | 10 2017-04-01 01:00:00 | 05 

and requests:

select      date_format(created_at,'%y-%m-%d %h:00:00') date,      count(id) total     requests     group hour( created_at ) 

the principle same, need average amount of items requests `(count of items/count of requests) grouped hour , don't know how it.

if want average, use avg():

select date_format(created_at, '%y-%m-%d %h:00:00') date,         avg(quantity) avg_quantity items group date(created_at), hour( created_at ); 

note: should not grouping hour without date -- unless want combine hours different days. seems unlikely because selecting entire date.