Find total date in ms sql 2008 - sql

Question

I need help to find a total day in ms sql 2008 for example I have a course table like following
+----------+------------+------------+
| Course | DateFrom | DateTo |
+----------+------------+------------+
| Course1a | 12/22/2015 | 12/22/2015 |
| Course1b | 12/22/2015 | 12/22/2015 |
| Course1c | 12/24/2015 | 12/28/2015 |
+----------+------------+------------+
and a Holiday table that store holiday which mean no course during that day
+-----------+------------+
| name | DateFrom |
+-----------+------------+
| Christmas | 12/25/2015 |
+-----------+------------+
In here I want to have total days for course1 to be 5 days (12/22, 12/24, 12/25(do not count christmas holiday), 12/26, 12/27, 12/28)

Answer 1

One way to achieve it is to use:
;WITH tally AS
(
SELECT TOP 1000 r = ROW_NUMBER() OVER(ORDER BY (SELECT 1)) - 1
FROM master..spt_values
), cte AS
(
SELECT Course, DATEADD(d, t.r, c.DateFrom) AS dat
FROM #courses c
JOIN tally t
ON DATEADD(d, t.r, c.DateFrom) <= c.DateTo
)
SELECT LEFT(Course, 7) AS Course_Name,
COUNT(DISTINCT dat) AS Total_Days
FROM cte c
LEFT JOIN #holidays h
ON c.dat = h.DateFrom
WHERE h.DateFrom IS NULL
GROUP BY LEFT(Course, 7);
LiveDemo
Output:
╔═════════════╦════════════╗
║ Course_Name ║ Total_days ║
╠═════════════╬════════════╣
║ Course1 ║ 5 ║
╚═════════════╩════════════╝
How it works:
tally generates number table (any method)
cte transforms date_from and date_to to multiple rows
join with holidays table to exclude holiday dates
GROUP BY LEFT(Course, 7) is workaround (your course name should be distinct without suffixes (a,b,c) or you need another column that indicates that 3 courses combined create one course)
COUNT only DISTINCT dates to get total days count