MySQL group by week - mysql

Question

I have a large number of records with a transaction datetime field going back several years. I would like to do a comparative analysis between the same timespan this year and last. How can I group by week over a 3 month range?
I'm running into problems using the YEARWEEK and WEEK functions because of the day the year 2012 starts of versus the day 2011 starts on.
Given that I have records with datetimes everyday from Jan 1st to the current day, and records with the same datetimes from the prior year, how can I group by week so the output is sums with dates like: 01/01/2011, 01/08/2011, 01/15/2011, etc., and 01/01/2012, 01/08/2012, 01/15/2012, etc.?
My query so far is as follows:
SELECT
DATE_FORMAT(A.transaction_date, '%Y-%m-%d') as date,
ROUND(sum(A.quantity), 3) AS quantity,
ROUND(sum(A.total_amount), 3) AS amount,
A.product_code,
D.fuel_type_code,
D.fuel_type_name,
C.customer_code,
C.customer_name
FROM
cl_transactions AS A
INNER JOIN
card AS B ON A.card_number=B.card_number
INNER JOIN
customer AS C ON B.customer_code=C.customer_code
INNER JOIN
fuel_type AS D ON A.fuel_type=D.fuel_type_code
WHERE
((A.transaction_date >= DATE_FORMAT(NOW() - INTERVAL 3 MONTH, '%Y-%m-01')) OR (A.transaction_date - INTERVAL 1 YEAR >= DATE_FORMAT(NOW() - INTERVAL 15 MONTH, '%Y-%m-01') AND A.transaction_date <= NOW() - INTERVAL 1 YEAR))
GROUP BY
A.transaction_date, fuel_type_code;
I would essentially like something that achieves the following pseudo-query:
GROUP BY
STARTING FROM THE OLDEST DATE (A.transaction_date + INTERVAL 6 DAY)

Answer 1

I started with an inner query using sqlvariables to build out from/to ranges for this year and last year of each respective start of year/month/day (ex: 2012-01-01 and 2011-01-01 respectively). From that, I'm also pre-formatting the date for final output so you have ONE master date basis for display reflecting that of whatever the "this year" week would be.
From that, I do a join to the transaction table where the transaction date is BETWEEN the respective start of current week and start of next week. Since date/time stamps include hour minute, 2012-01-01 by itself is implied as 12:00:00am (midnight) of the day. and between will go UP TO 7 days later 12:00:00 am. And that date will become the start date of the following week.
So, by joining on the date being between EITHER last yr or this yr time period, its the same group qualification. So the field selection does a ROUND( SUM( IF() )) per respective last year or this year. if the incoming transaction date is LESS than the current year's week start, then it must be a record from prior year, otherwise its for the current year. So, respectively, add the value itself, or zero as it applies.
So now, you have the group by. The week that it qualified for was already prepared from the inner query via "ThisYearWeekOf" formatted column, regardless of the otherwise computed "YEARWEEK()" or "WEEK()". The date ranges took care of that qualification for us.
Finally, I added the fuel-type as a join and included that as the group by. You have to group by all non-aggregate columns for proper SQL, although MySQL lets you get by by just grabbing the first entry for the given group if it is NOT so specified in group by.
To close, I DID include the information for the customer as you didn't have it in the group by and did not appear to be applicable... it would just arbitrarily grab one. However, I've added it to the group by, so now your records will show at the per customer level, per product and fuel type, how much sales and quantity between this year and last.
SELECT
JustWeekRange.ThisYearWeekOf,
CTrans.product_code,
FT.fuel_type_code,
FT.fuel_type_name,
C.customer_code,
C.customer_name,
ROUND( SUM( IF( CTrans.transaction_date < JustWeekRange.ThisYrWeekStart, CTrans.Quantity, 0 )), 3) as LastYrQty,
ROUND( SUM( IF( CTrans.transaction_date < JustWeekRange.ThisYrWeekStart, CTrans.total_amount, 0 )), 3) as LastYrAmt,
ROUND( SUM( IF( CTrans.transaction_date < JustWeekRange.ThisYrWeekStart, 0, CTrans.Quantity )), 3) as ThisYrQty,
ROUND( SUM( IF( CTrans.transaction_date < JustWeekRange.ThisYrWeekStart, 0, CTrans.total_amount )), 3) as ThisYrAmt,
FROM
( SELECT
DATE_FORMAT(#ThisYearDate, '%Y-%m-%d') as ThisYearWeekOf,
#LastYearDate as LastYrWeekStart,
#ThisYearDate as ThisYrWeekStart,
#LastYearDate := date_add( #LastYearDate, interval 7 day ) LastYrStartOfNextWeek,
#ThisYearDate := date_add( #ThisYearDate, interval 7 day ) ThisYrStartOfNextWeek
FROM
(select #ThisYearDate := '2012-01-01',
#LastYearDate := '2011-01-01' ) sqlvars,
cl_transactions justForLimit
HAVING
ThisYrWeekStart < '2012-04-01'
LIMIT 15 ) JustWeekRange
JOIN cl_transactions AS CTrans
ON CTrans.transaction_date BETWEEN
JustWeekRange.LastYrWeekStart AND JustWeekRange.LastYrStartOfNextWeek
OR CTrans.transaction_date BETWEEN
JustWeekRange.ThisYrWeekStart AND JustWeekRange.ThisYrStartOfNextWeek
JOIN fuel_type FT
ON CTrans.fuel_type = FT.fuel_type_code
JOIN card
ON CTrans.card_number = card.card_number
JOIN customer AS C
ON card.customer_code = C.customer_code
GROUP BY
JustWeekRange.ThisYearWeekOf,
CTrans.product_code,
FT.fuel_type_code,
FT.fuel_type_name,
C.customer_code,
C.customer_name