1ヶ月おきの累計売上高をMySQLで集計し、Excelでグラフにする ref: http://qiita.com/ryuichi69/items/ba0858c3af977adff418

practice_table.sql

CREATE TABLE IF NOT EXISTS `tbl` (
  `id` int(10) NOT NULL COMMENT '主キー',
  `time` datetime NOT NULL COMMENT '集計日',
  `sales` int(100) NOT NULL COMMENT 'その日の売上高'
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

practice_table_data.sql

INSERT INTO `tbl` (`id`, `time`, `sales`) 
VALUES 
(NULL, '2016-01-04 12:00:00', '1000000'), 
(NULL, '2016-02-10 13:00:00', '1400000'), 
(NULL, '2016-02-25 15:00:00', '600000'), 
(NULL, '2016-03-04 16:00:00', '800000'), 
(NULL, '2016-03-25 18:00:00', '800000'), 
(NULL, '2016-04-20 09:00:00', '500000'), 
(NULL, '2016-04-29 14:00:00', '400000'), 
(NULL, '2016-05-11 00:00:00', '700000'), 
(NULL, '2016-05-30 15:00:00', '300000'), 
(NULL, '2016-06-22 17:00:00', '1200000');

sales_per_month.sql

SELECT 
    date_format(a.time,'%Y-%m') as dt,
    sum(a.sales),
    (
    SELECT 
        sum(b.sales) 
        FROM 
        tbl b 
        WHERE
            date_format(b.time, '%Y-%m') <= date_format(a.time,'%Y-%m') 
            and 
            date_format(b.time,'%Y-%m') >= '2016-01'
    ) 
    as total 
from 
    tbl a 
where 
    a.time between '2016-01-01 00:00:00' and '2016-12-31 23:59:59' 
group by dt