Changing start-date in MySQL for week - mysql

Question

I found the following code to help in creating a weekly report based on a start date of Friday. The instructions say to replace ".$startWeekDay." with a 4. When I put '".$startDay."' as '2013-01-30', I get errors.
Also I get a report by day rather than week as I desire.
SELECT SUM(cost) AS total,
CONCAT(IF(date - INTERVAL 6 day < '".$startDay."',
'".$startDay."',
IF(WEEKDAY(date - INTERVAL 6 DAY) = ".$startWeekDay.",
date - INTERVAL 6 DAY,
date - INTERVAL ((WEEKDAY(date) - ".$startWeekDay.")) DAY)),
' - ', date) AS week,
IF((WEEKDAY(date) - ".$startWeekDay.") >= 0,
TO_DAYS(date) - (WEEKDAY(date) - ".$startWeekDay."),
TO_DAYS(date) - (7 - (".$startWeekDay." - WEEKDAY(date)))) AS sortDay
FROM daily_expense
WHERE date BETWEEN '".$startDay."' AND '".$endDay."'
GROUP BY sortDay;
The following code is what I am using
SELECT count(DISTINCT (
UserID)
) AS total, CONCAT(IF(date(LastModified) - INTERVAL 6 day < date(LastModified),
date(LastModified),
IF(WEEKDAY(date(LastModified) - INTERVAL 6 DAY) = 4,
date(LastModified) - INTERVAL 6 DAY,
date(LastModified) - INTERVAL ((WEEKDAY(date(LastModified)) - 4)) DAY)),
' - ', date(LastModified)) AS week
FROM `Purchase`
WHERE `OfferingID` =87
AND `Status`
IN ( 1, 4 )
GROUP BY week
The output I get is
total week
3 2013-01-30 - 2013-01-30
1 2013-01-31 - 2013-01-31

Answer 1

I'm not sure exactly how you want to display your week, the sql above is attempting to display date ranges. If this isn't a requirement, your query could be very simple, you can just offset your time by two days (since friday is two days away from the natural star of the week) and use the week function to get the week number.
The query would look like this:
select count(distinct (UserID)) as total
, year( LastModified + interval 2 day ) as year
, week( LastModified + interval 2 day ) as week_number
FROM `Purchase`
WHERE `OfferingID` =87
AND `Status`
IN ( 1, 4 )
group by year, week_number;