SUM multiple date ranges in mysql query - php

Question

I have a MySql table 'Products' with three columns:
Date | Product | Qty
My aim is to SUM the qty of each product for every week.
Getting the SUM between two given dates would be easy:
SELECT SUM(qty) FROM products WHERE date >= '2010-01-01' AND date < '2011-01-1'
I can generate a list of weeks in Php using something like:
$today = date('Y-m-d', strtotime('last week Monday'));
$future = date('Y-m-d', strtotime('+90 days'));
$period = new DatePeriod(
new DateTime($today),
new DateInterval('P7D'),
new DateTime($future)
);
foreach ($period as $key => $value) {
$dates .= $value->format('Y-m-d');
}
Is there a MySql query that would work to Group By and SUM by dates? Or would I be better off looping through in Php?

Answer 1

You can use Year() and Week() functions in MySQL, to get the year and week number for a given date. Week() function will return week number from 0 to 53. So, you will be needed to use Year() function alongwith, if you have data spanning over multiple years.
But then, you will be more interested in knowing the start date and end date for the concerned week. This is where we can use a very interesting function DayOfWeek(). It returns the weekday index for a given date (1 = Sunday, 2 = Monday, …, 7 = Saturday)
We can use Date_Add() function using the weekday index value and the actual date value, to determine the starting week date and ending week date for a given date.
Try the following (if the Week starts on Sunday) :
SELECT
DATE_ADD(`date`, INTERVAL(1 - DAYOFWEEK(`date`)) DAY) AS week_start_date,
DATE_ADD(`date`, INTERVAL(7 - DAYOFWEEK(`date`)) DAY) AS week_end_date,
SUM(qty)
FROM
products
GROUP BY week_start_date, week_end_date
If the week starts on Monday, another handy function is WeekDay(). It returns the weekday index for date (0 = Monday, 1 = Tuesday, … 6 = Sunday).
Try the following (if the Week starts on Monday) :
SELECT
DATE_ADD(`date`, INTERVAL(0 - WEEKDAY(`date`)) DAY) AS week_start_date,
DATE_ADD(`date`, INTERVAL(6 - WEEKDAY(`date`)) DAY) AS week_end_date,
SUM(qty)
FROM
products
GROUP BY week_start_date, week_end_date

Answer 2

You can achieve that with a group by like
GROUP BY week(date)

Answer 3

GROUP BY so do
SELECT SUM(qty) FROM products GROUP BY WEEK(date);