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

I did it my own way checking other answers here on Stackoverflow, it should work:

select sum(months)
from (select t.*, 
         @time := if(@sum = 0, 0, period_diff(date_format(start_date, '%Y%m'), date_format(@prevtime, '%Y%m'))) as months,
         @prevtime := start_date,
         @sum := @sum + isstart
  from ((select start_date, 1 as isstart
         from position t
        ) union all
        (select end_date, -1
         from position t
        )
       ) t cross join
       (select @sum := 0, @time := 0, @prevtime := 0) vars 
  order by 1, 2
 ) t