"neater" way of counting holidays - sql-server-2008

Question

I have a neat table of holidays showing date and recurrence if such holiday is recurrent (i.e. New Year)
Now, I need to count the number of holidays between two dates. If it was a simple list of dates without info about recurrence (so i.e. it would show all New Years between 2000-01-01 and 2015-01-01) it would be quite easy, i.e. something like
declare #start_Date Date= '2013-01-02',
#end_date Date ='2014-01-02'
SELECT COUNT(CE.name) AS holidays_count
FROM dbo.argo_cal_event AS CE INNER JOIN dbo.argo_cal_event_type AS CET
ON CE.event_type_gkey = CET.gkey
WHERE (CET.name = 'EXEMPT_DAY') AND (CE.name <> 'Sundays')
AND (CE.occ_start BETWEEN #start_Date AND #end_date)
But now we have a neat recurrence, so the query above won't count all the New Years, Christmases etc that have been declared as happening "every year starting from".
I COULD create a table with such list, but I've been wondering, is there any other way?
EDIT: Let me precise what I had in mind: I'd like to count the event normally if it event occurs once (I will assume here that user will have to populate all the irregular holidays as i.e. Easter), but when the recurrence <> Once, then get the occurrence start and count the years between that date and final date.
EDIT2: I think I've got it - for the recurrent holidays I can use
SELECT sum (datediff (year, ce.occ_start, #end_date)) as recurrent_holidays
FROM dbo.argo_cal_event AS CE INNER JOIN dbo.argo_cal_event_type AS CET
ON CE.event_type_gkey = CET.gkey
WHERE (CET.name = 'EXEMPT_DAY') and (CE.repeat_interval ='ANNUALLY')
EDIT3: unfortunately this solution doesn't work (or at least getting quite complicated) if I'd like to count between TWO dates, in which one is taken from another table, i.e if I'd like to count recurring holidays between unit.time_in and getddate() :/

Answer 1

The most straightforward way would be to make them all one-time occurrences.
The table isn't going to be that big that you can't add in every Sunday. It's only 52 or 53 entries per year.
If you do it this way now you can do something like,
select count(*) from events where event_date between start_date and end_date
Done.
The main reason to do it this way, though, is that some of your holidays are tricky to calculate. You'll need to be calculating (or looking up) the dates for Good Friday, Easter Monday, and others. They're based on the phase of the moon.
Why not just calculate them all and make your query really easy?
In the end, it matters a lot less how "neat" your data structures are and a lot more on whether your code does what it's supposed to do, how long it takes to do it, and how much effort it takes to get it working.

Answer 2

You could create a function that searches your holiday table for holidays of each type (weekly, monthly, yearly, one-off, etcetera) or even "Nth/Last/Nth Last Whateverday of Whichevermonth" (which would be a variant on Yearly), and for each holiday, interval by interval, loops through and increments each holiday date and checks if it falls between the StartDate and EndDate dates that the function would need to take as parameters. You could even find an Easter Date calculation algorithm and insert that too.
However, such a function wouldn't be simple or as fast as a simple Select statement - you need to decide whether it is worth expending the time and effort to develop such a function and the performance penalty it could impose on your queries is worth the flexibility it would give you and your users.
Almost anything can be done; you should also ask if it should be done...

Answer 3

One terrible approach:
declare #Holidays as Table ( Name VarChar(16), OccurrenceStart Date, Recurrence VarChar(10) );
insert into #Holidays ( Name, OccurrenceStart, Recurrence ) values
( 'New Year Day', '20000101', 'Annually' ),
( 'Sundays', '20000202', 'Weekly' ),
( 'Labour Day 2014', '20141027', 'Once' );
select * from #Holidays;
declare #Start as Date = '20130102';
declare #End as Date = '20150101';
with DateRange as ( -- All dates from #Start to #End .
select #Start as ADate
union all
select DateAdd( day, 1, DR.ADate )
from DateRange as DR
where DR.ADate < #End ),
Once as ( -- Holidays that occur once within the date range.
select DR.ADate as Holiday
from DateRange as DR inner join
#Holidays as H on H.OccurrenceStart = DR.ADate and H.Recurrence = 'Once' ),
Weekly as ( -- Holidays that occur weekly within the date range, give or take.
select DateAdd( week, case when H.OccurrenceStart < #Start then DateDiff( week, H.OccurrenceStart, #Start ) else 0 end, H.OccurrenceStart ) as Holiday
from #Holidays as H
where H.OccurrenceStart <= #End and H.Recurrence = 'Weekly'
union all
select DateAdd( week, 1, W.Holiday )
from Weekly as W
where DateAdd( week, 1, W.Holiday ) <= #End ),
Annually as ( -- Holidays that occur annually within the date range, give or take.
select DateAdd( year, case when H.OccurrenceStart < #Start then DateDiff( year, H.OccurrenceStart, #Start ) else 0 end, H.OccurrenceStart ) as Holiday
from #Holidays as H
where H.OccurrenceStart <= #End and H.Recurrence = 'Annually'
union all
select DateAdd( year, 1, A.Holiday )
from Annually as A
where DateAdd( year, 1, A.Holiday ) <= #End )
select Count( 42 ) as 'Number of Holidays'
from DateRange as DR inner join
( select Holiday from Once union
select Holiday from Weekly union
select Holiday from Annually ) as H on H.Holiday = DR.ADate
option ( MaxRecursion 0 );
Note that multiple 'hits' on one day, e.g. New Years Day falling on a Sunday, are counted as a single holiday. There are more efficient ways to generate DateRange, e.g. with a numbers table. And the whole thing is hideous.
Ask and ye shall be deceived.