How to make a time dependent distribution in SQL? -

i have sql table in keep project information coming primavera. suppose have columns start date,end date,duration, , total qty shown below . how can distribute total qty on months using these information. kind of additional columns, sql queries need in order correct monthly distribution?

thanks in advance.

columns in order:

itemname,quantity,startdate,duration,enddate  item1 -- 108 -- 2013-03-25 -- 720 -- 2013-07-26  item2 -- 640 -- 2013-03-25 -- 720 -- 2013-07-26   .   . 

i think key break records apart month. here example of how it:

with months (      select 1 mon union select 2 union select 3 union      select 4 mon union select 5 union select 6 union      select 7 mon union select 8 union select 9 union      select 10 mon union select 11 union select 12     ) select item, m.mon, quantity / nummonths (select t.*, (month(enddate) - month(startdate) + 1) nummonths       t      ) t join      months m      on month(t.startdate) <= m.mon ,         months(t.enddate) >= m.mon; 

this works because months within same year -- in example. quite vague on how split should calculated. so, assumed every month start end gets equal amount.