Summing range of dates without counting overlaps in mysql

Question

I have simple table with start_date and end_date columns in it. These date values may overlap

id    start_date    end_date
1     2011-0         


        

Answer 1

If you need the total periods for a number of records including the overlaps, then simply sum the period differences per record:

SELECT SUM(PERIOD_DIFF( DATE_FORMAT(end_date, '%Y%m') , DATE_FORMAT(start_date, '%Y%m') )) AS total_periods
FROM table WHERE ...