select request_count,response_count, (response_count*100) / (request_count+response_count) AS proportion from total_dummy_table;

select request_count,response_count, 
case 
    when 
    request_count+response_count = 0 then 0 
    else
(response_count*100) / (request_count+response_count) 
end
AS proportion 
from
total_dummy_table;

SELECT CAST((
SELECT CAST(COUNT(a.w_operation_id) AS real) 
FROM warehousing a, product b, producer c 
WHERE 
	a.pt_id = b.pt_id AND 
	b.pr_id = c.pr_id AND 
	c.pr_regularity='t' AND 
	a.w_date_out='2015-02-15'
)/(
SELECT CAST(COUNT(a.w_operation_id) AS real) 
FROM warehousing a, product b, producer c 
WHERE 
	a.pt_id = b.pt_id AND 
	b.pr_id = c.pr_id AND 
	a.w_date_out='2015-02-15') AS real
) AS result;