SQL Count sickness days - sql

Question

I have a SQL Server table which contains the list of all staff and their sickness.
I need to be able to calculate how many days they have had sick in the current quarter
The issue is, some people may have been sick for a year so, E.G the FROMDATE could be 2013-12-31 and the UNTILDATE could be 2014-12-31 (1 year sickness leave). However it should only count the days from that sickness that occur in the current quarter. So it should be around 90 days of sickness rather than count the entire year.
Current SQL
select SUM(a.WORKDAYS) as Total
from ABSENCE a
where a.FROMDATE < GETDATE() and
a.UNTILDATE > DATEADD(MONTH, -3, GETDATE())
and
a.ABS_REASON='SICK'
So at the moment, it takes from any fromdate which is correct as I need to account for people who were already sick before the quarter started but still sick going into the current quarter but should only count the number of days from when the quarter started until the end of the quarter.
Any help would be greatly appreciated.

Answer 1

With a table of dates, you could easily find the count of dates where the date is between your two dates of interest, and where there exists a leave period that surrounds it. You could also filter your dates to exclude non-business days and public holidays.
There are lots of ways to generate such a table of dates, and plenty described both on stackoverflow and dba.stackexchange.

Answer 2

Not sure about your columns.you should only provide sql that gives records between 2013-12-31 and 2014-12-31 and then ask your problem .
Try this,
select SUM(Case when datepart(MM, a.FROMDATE) IN (10,11,12) Then a.WORKDAYS Else End)
as Total
from ABSENCE a
where a.FROMDATE >= '2013-12-31' and
a.UNTILDATE <= '2014-12-31'
and
a.ABS_REASON='SICK'

Answer 3

SELECT SUM(a.WORKDAYS) as Total
FROM ABSENCE a
WHERE (a.FROMDATE >= DATEADD(MONTH, -3, GETDATE()) OR a.UNTILDATE >= DATEADD(MONTH, -3, GETDATE()))
AND a.ABS_REASON = 'SICK'
Quarter Specific
SELECT SUM(a.WORKDAYS) as Total
FROM ABSENCE a
WHERE (a.FROMDATE >= DATEADD(quarter, -1, GETDATE()) OR a.UNTILDATE >= DATEADD(quarter, -1, GETDATE()))
AND a.ABS_REASON = 'SICK'

Answer 4

Having a Calendar table with the list of all possible dates is handy, but in this case we can do without it.
I'll generalize your question a bit. Instead of looking just at the current quarter let's have two parameters that define the range of dates that you are interested in:
DECLARE #ParamStartDate date;
DECLARE #ParamEndDate date;
At first we need to get all rows from Absence that have a range from FromDate to UntilDate that intersects with the given period.
SELECT
...
FROM
Absence
WHERE
ABS_REASON='SICK'
-- all absence periods, which overlap with the given period
AND FromDate <= #ParamEndDate
AND UntilDate >= #ParamStartDate
Two periods A and B overlap when (StartA <= EndB) and (EndA >= StartB).
Then we need to calculate how many days are in the intersection of the two periods.
The intersection period can't be larger than the given range of dates (#ParamStartDate to #ParamEndDate).
The intersection period can't be larger than the duration of the sickness (FromDate to UntilDate).
So, the beginning of the intersection is the latest of FromDate and #ParamStartDate, i.e. MAX(FromDate, #ParamStartDate)
The ending of the intersection is the earliest of UntilDate and #ParamEndDate, i.e. MIN(UntilDate, #ParamEndDate)
Finally, the duration of the intersection in days is
DATEDIFF(day, MAX(FromDate, #ParamStartDate), MIN(UntilDate, #ParamEndDate))
But, only if it is positive. If it is negative, it means that sickness period ended before the given quarter started (or sickness started after the given quarter ended).
There is no built-in MIN, MAX functions that take two parameters as I need, so I use CROSS APPLY to calculate them. Also, I calculate the number of days in the given quarter, just for completeness. The final query looks like this:
SELECT
1+DATEDIFF(day, #ParamStartDate, #ParamEndDate) AS QuarterDays
,CASE WHEN 1+DATEDIFF(day, CTE_MaxStartDate.AbsenceStartDate, CTE_MinEndDate.AbsenceEndDate) > 0
THEN 1+DATEDIFF(day, CTE_MaxStartDate.AbsenceStartDate, CTE_MinEndDate.AbsenceEndDate)
ELSE 0 END AS AbsenceDays
FROM
Absence
CROSS APPLY
(
SELECT CASE WHEN UntilDate < #ParamEndDate THEN UntilDate ELSE #ParamEndDate END AS AbsenceEndDate
) AS CTE_MinEndDate
CROSS APPLY
(
SELECT CASE WHEN FromDate > #ParamStartDate THEN FromDate ELSE #ParamStartDate END AS AbsenceStartDate
) AS CTE_MaxStartDate
WHERE
ABS_REASON='SICK'
-- all absence periods, which overlap with the given period
AND FromDate <= #ParamEndDate
AND UntilDate >= #ParamStartDate
I add 1 to DATEDIFF to get a duration of one day if start and end dates of the period are the same.