Create a ROLLING sum over a period of time in mysql

Question

I have a table with columns date and time_spent. I want to find for each date D the sum of the values of \'time_spent\' for the period of time : (D

Answer 1

Here is another solution

SELECT r1.date, r1.time_spent, 
   ( SELECT SUM(time_spent) 
     FROM rolling_total AS r2
     WHERE datediff(r1.date, r2.date) 
     BETWEEN 0 AND 7
   ) AS rolling_week_total
FROM rolling_total AS r1  
ORDER BY r1.date
LIMIT 8