MySQL GROUP BY WEEK Starting 1st of month - mysql

Question

Need to GROUP BY WEEKS Starting from 1st of current month
DDLs:
CREATE TABLE `group_by_week` (
`id` int(4) NOT NULL AUTO_INCREMENT,
`date` date DEFAULT NULL,
`value` int(4) DEFAULT NULL,
PRIMARY KEY (`id`)
);
INSERT INTO `group_by_week`
(`date`,`value`)
VALUES
('2016-01-01',1),
('2016-01-02',2),
('2016-01-03',3),
('2016-01-04',4),
('2016-01-05',5),
('2016-01-06',6),
('2016-01-07',7),
('2016-01-08',8),
('2016-01-09',9),
('2016-01-10',10),
('2016-01-11',11),
('2016-01-12',12),
('2016-01-13',13),
('2016-01-14',14),
('2016-01-15',15),
('2016-01-16',16);
EXPECTED RESULT:
week 1 => 28
week 2 => 77
week 3 => 31

Answer 1

You may need to get the week number by diving the Day part with 7 and then you may need to round the result using FLOOR.
If dates from different months are there, then its better to add month name along with the week number. So I just did that way. So the first column values would be like monthname weeknumber. And we can group by with the same first column.
Query
SELECT
CONCAT(MONTHNAME(`date`), ' week ', FLOOR(((DAY(`date`) - 1) / 7) + 1)) `month & week`,
SUM(`value`) AS `value`
FROM `group_by_week`
GROUP BY `month & week`
ORDER BY month(`date`), `month & week`;
Result
+-----------------+-------+
| month & week | value |
+-----------------+-------+
| January week 1 | 28 |
| January week 2 | 77 |
| January week 3 | 31 |
+-----------------+-------+
SQL Fiddle Demo

Answer 2

E.g.:
SELECT CEILING(DATE_FORMAT(date,'%d')/7) w
, SUM(value) week_total
FROM group_by_week
GROUP
BY w;
Obviously, you need to extend the logic a little if dealing with more than one month, but I'll leave that as an exercise for the reader.
Note also that the '4' in 'INT(4)' is fairly meaningless - I doubt very much that it does whatever you think it does.