SQL - date group by year, month, days - update - sql

Question

I used code to calculate difference between two date group by year, months, date:
;WITH calendar AS (
SELECT CAST(MIN([From date]) as datetime) as d,
MAX([To date]) as e
FROM ItemTable
UNION ALL
SELECT DATEADD(day,1,d),
e
FROM calendar
WHERE d < e
), cte AS(
SELECT i.Item,
DATEPART(year,c.d) as [Year],
DATEDIFF(month,MIN(c.d),MAX(c.d)) as NoOfMonth,
DATEDIFF(day,DATEADD(month,DATEDIFF(month,MIN(c.d),MAX(c.d)),MIN(c.d)),
MAX(c.d)) as NoOfDays
FROM ItemTable i
INNER JOIN calendar c
ON c.d between i.[From date] and i.[To date]
GROUP BY i.Item, DATEPART(year,c.d),[From date],[To date]
)
SELECT Item,
[Year],
SUM(NoOfMonth) as NoOfMonth,
SUM(NoOfDays) as NoOfDays
FROM cte
GROUP BY Item,[Year]
ORDER BY Item
OPTION (MAXRECURSION 0)
I found this code in SQL - date group by year, month, days
But not work for me...
When I execute my query
SELECT Item,
[From date],
[To date]
from ItemDate;
I got
('A1','2013-08-27','2013-09-27'),
('A1','2013-09-28','2013-11-28'),
('A1','2013-11-30','2013-12-03'),
('A1','2013-12-31','2014-03-31'),
('A1','2014-04-01','2014-07-01'),
('A1','2014-07-02','2014-10-02'),
('A1','2014-10-03','2014-12-31')
and when execute code from this link SQL - date group by year, month, days
I get this:
Item Year NoOfMonth NoOfDays
A1 2013 4 -27
A2 2014 10 58
This is not good.... It should be 3 months and 4 day for year 2013,
and for year 2014 11 month and 28 days
How to update the code to get the desired result?

Answer 1

Change the last select to:
SELECT Item,
[Year],
CASE WHEN SUM(NoOfDays) < 0 THEN SUM(NoOfMonth)-1
WHEN SUM(NoOfDays) > 30 THEN SUM(NoOfMonth)+1
ELSE SUM(NoOfMonth) END as NoOfMonth,
CASE WHEN SUM(NoOfDays) >= 30 THEN SUM(NoOfDays)-30
WHEN SUM(NoOfDays) < 0 THEN SUM(NoOfDays)+30
ELSE SUM(NoOfDays) END as NoOfDays
FROM cte
GROUP BY Item,[Year]
ORDER BY Item
OPTION (MAXRECURSION 0)
The main problem of such report - it is hard to define what is 1 month, DATEDIFF just takes number from 2 dates and subtract one from another.
I have choose 30 as a days count in month, and now I compare values of days with 30 so we can add +1 to month if the day count goes under zero or below 30