Count periods and duration of sick within a rolling 12 Month - sql-server

Question

I'm fairly new to SQL and find this site to be a brilliant resource. I'm hoping for a little bit of help with a task I've been assigned.
Basically I need to find the number of periods of sickness a member of staff has taken in the last 12 month and the duration of each period of sickness.
I have a simple table that looks like this:
Agent Date Status
A 01/07/2015 SHIFT
A 02/07/2015 SHIFT
A 03/07/2015 SICK
A 04/07/2015 SHIFT
A 05/07/2015 SHIFT
A 06/07/2015 SHIFT
B 01/07/2015 SICK
B 02/07/2015 SICK
B 03/07/2015 SHIFT
B 04/07/2015 SHIFT
B 05/07/2015 SICK
B 06/07/2015 SICK
C 01/07/2015 SHIFT
C 02/07/2015 SHIFT
C 03/07/2015 SICK
C 04/07/2015 SICK
C 05/07/2015 SICK
C 06/07/2015 SHIFT
I'm hoping someone can help me find some code that would produce the following kind of output:
Agent Days
A 1
B 2
B 2
C 3
Any help would be greatly appreciated.
Cheers

Answer 1

For sql-server:
select count(1) from TableA
where Status = 'SICK' and Date >= CAST(DATEADD(MONTH, -12, CURRENT_TIMESTAMP) AS DATE)
group by Agent
Grouped by periods of sickness:
WITH Cte AS(
SELECT *,
DATEDIFF(dd, '12/30/1899', [Date]) as [number],
RN = DATEDIFF(dd, '12/30/1899', [Date]) - ROW_NUMBER()
OVER(PARTITION BY Agent ORDER BY DATEDIFF(dd, '12/30/1899', [Date]))
FROM TableA
WHERE
[Status] = 'SICK' and
[Date] >= CAST(DATEADD(MONTH, -12, CURRENT_TIMESTAMP) AS DATE)
)
,CteFinal AS(
SELECT
Agent,
startNumber = MIN(number),
endNumber = MAX(number)
FROM Cte
GROUP BY Agent, RN
)
select Agent, endNumber - startNumber +1 as [Days] from CteFinal
group by agent, startNumber, endNumber
Sqlfiddle
In addition, for case with days off in table TableB:
WITH Cte AS(
SELECT distinct *,
DATEDIFF(dd, '12/30/1899', [Date]) as [number],
RN = DATEDIFF(dd, '12/30/1899', [Date]) - ROW_NUMBER()
OVER(PARTITION BY Agent ORDER BY DATEDIFF(dd, '12/30/1899', [Date]))
FROM (select distinct * from TableA
union all
select distinct Agent, b.Date, 'DAY OFF' from TableA cross join TableB b) TableA
WHERE
[Status] IN ('SICK', 'DAY OFF') and
[Date] >= CAST(DATEADD(MONTH, -12, CURRENT_TIMESTAMP) AS DATE)
)
,CteFinal AS(
SELECT
Agent,
startNumber = MIN(number),
endNumber = MAX(number),
dayOffs = SUM(CASE WHEN [Status] = 'DAY OFF' THEN 1 ELSE 0 END)
FROM Cte
GROUP BY Agent, RN
)
select Agent, endNumber - startNumber +1 - sum(dayOffs) as [Days] from CteFinal
group by agent, startNumber, endNumber
having(endNumber - startNumber +1 - sum(dayOffs) > 0)
Sqlfiddle