MYSQL Daily Data Compare Last Week vs Two Weeks Ago - mysql

Question

I have daily data for multiple locations that we need to compare last week total sales with total sales 2 weeks ago. Here is the MYSQL code
SELECT
name,
SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales ELSE NULL END) as 'Last Week',
SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales ELSE NULL END) as '2 Weeks Ago',
SUM('1week' - '2week') AS 'Change'
FROM daily_sales
GROUP BY name
The output for the 1st three columns is correct, but I cannot get the 4th column "change" to calculate correctly. Tried SUM of the cases but could not get over invalid use og group function:
SUM((SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales ELSE NULL END))
- (SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales ELSE NULL END))) AS 'change'
Help!

Answer 1

You're almost there; just take the formula that give cols 2 and 3 and put a minus between them:
SELECT
name,
SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales END) as LastWeek,
SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales END) as TwoWeeksAgo,
SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales END) - SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales END) as change
FROM daily_sales
WHERE date >= date_sub(now(), interval 3 week)
GROUP BY name
Or by use of a subquery:
SELECT name, lastweek, twoweeksago, lastweek - twoweeksago as change
FROM
(
SELECT
name,
SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales END) as LastWeek,
SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales END) as TwoWeeksAgo
FROM daily_sales
WHERE date >= date_sub(now(), interval 3 week)
GROUP BY name
) x
Or by use of a cte:
WITH x AS(
SELECT
name,
SUM(CASE WHEN WEEK(date) = WEEK(now())-1 THEN sales END) as LastWeek,
SUM(CASE WHEN WEEK(date) = WEEK(now())-2 THEN sales END) as TwoWeeksAgo
FROM daily_sales
WHERE date >= date_sub(now(), interval 3 week)
GROUP BY name
)
SELECT name, lastweek, twoweeksago, lastweek - twoweeksago as change