SQL Server 2008 Count(Distinct CASE? - sql

Question

SELECT
ScheduleDays = COUNT(DISTINCT(CAST(datediff(d, 0, a.ApptStart) AS datetime)))
FROM
Appointments a
WHERE
ApptKind = 1 AND
--filter on current month
a.ApptStart >= ISNULL(DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0),'1/1/1900') AND
a.ApptStart < ISNULL(DATEADD(month, DATEDIFF(month, 0, GETDATE())+1, 0),'1/1/3000')AND
--filter all days that aren't Friday, and then give you all Fridays that have an hour > 12.
DATENAME(weekday, a.ApptStart) <> 'Friday' and DATEPART(hour, a.ApptStart) > 12 AND
--Filter on doctor
a.ResourceID in (201)
This query will look through appointment start times and not count Fridays as our Docs only work a half day on Fridays. I was told that we do want to count them, but only as half days (first time around I was told to exclude them lol).
Could someone please help me with a Case statement that will count Fridays that do not have an appointment after 12noon, as half a day? I believe it will have to go in the ScheduleDays=COUNT(DISTINCT(CAST(datediff(d,0,a.ApptStart) as datetime))). Perhaps we can put the Friday and after 12 filters in there instead of in the where clause if we are going to use case anyways. ScheduleDays=COUNT(DISTINCT CASE WHEN etc. I really appreciate the help.

Answer 1

You can't really count half things using count, so that is not the way to go. But, you can do it with arithmetic. I think something like this:
select (count(distinct (case when DATENAME(weekday, a.ApptStart) <> 'Friday'
then cast(a.apptstart as date)
end)
) +
0.5 * count(distinct (case when DATENAME(weekday, a.ApptStart) = 'Friday'
then cast(a.apptstart as date)
end)
)
) as ScheduleDays
If the docs only work on Fridays for half a day, I don't think you need to check for the time of the appointment. Of course, you can if you like by adding it into the second count.
Note that to count days, I used the simpler syntax of casting the datetime to a date.
EDIT:
With the hour check:
select (count(distinct (case when DATENAME(weekday, a.ApptStart) <> 'Friday'
then cast(a.apptstart as date)
end)
) +
0.5 * count(distinct (case when DATENAME(weekday, a.ApptStart) = 'Friday' and DATEPART(hour, a.ApptStart) <= 12
then cast(a.apptstart as date)
end)
)
) as ScheduleDays