How to get the running total for data grouped by month for a MySQL query
SET @running_total:=0;
select
xx.*,
(@running_total := @running_total + xx.total) AS running_total
from (
select count(id) total, concat(concat(year(created_at), '-', lpad(month(created_at), 2, '0'))) year_month
from users
where created_at is not null group by year_month order by year_month
) as xx;
From http://stackoverflow.com/questions/664700/calculate-a-running-total-in-mysql