Get data grouped by 12 weeks period - mysql

Question

I have a table with orders data:
CREATE TABLE `orders` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL DEFAULT '0',
`price` decimal(6,3) unsigned NOT NULL,
`created` datetime DEFAULT NULL,
`paid` datetime DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;
I need to get price sum of orders in 12 weeks periods, where first period starts on a week when the very first order was paid, and each next period starts one week later than previous (this to have possibility to compare data in 12 weeks periods). So eventually there must be periods like 1-12, 2-13, etc.
Important detail: I can't use variables in query, because this query will be used in BI Tool, where queries with variables behave unexpected.

Answer 1

Did it next way:
SELECT `periods`.*, SUM(`orders`.`price`) AS `revenue`
FROM (SELECT DISTINCT FROM_DAYS(TO_DAYS(`paid`) - MOD(TO_DAYS(`paid`) -1, 7)) AS `period_start`,
(FROM_DAYS(TO_DAYS(`paid`) - MOD(TO_DAYS(`paid`) -1, 7)) + INTERVAL 12 WEEK) AS `period_end`
FROM `orders`
) AS `periods`
LEFT JOIN `orders` ON DATE(`orders`.`paid`) BETWEEN `periods`.`period_start` AND `periods`.`period_end`
GROUP BY `periods`.`period_end`
Small explanation: at first I define 12 week periods in subquery, using same table data. By doing this
DISTINCT FROM_DAYS(TO_DAYS(`paid`) - MOD(TO_DAYS(`paid`) -1, 7))
I shift paid value to the beginning of week.
With this
(FROM_DAYS(TO_DAYS(`paid`) - MOD(TO_DAYS(`paid`) -1, 7)) + INTERVAL 12 WEEK)
I add 12 weeks to the date means beginning of week.
Eventually I get result like this:
| period_start | period_end |
| 2015-07-19 | 2015-10-11 |
| 2015-07-26 | 2015-10-18 |
Then I simply join orders table and group data by end of period.
Looks like it does what I need.