SQL Calculate 20 business days, remove bank hols and reference to another query - sql

Question

Sorry I am quite new to creating functions in SQL Server 2008 R2. I have largely been able to get by using T-SQL statements.
However I need to create a report that returns records with a date (program start date), that part is simple enough, however for each row date I want to calculate a target completion date based on 20 business days. I also want to avoid counting bank holidays too. I have a table named dCalendar which holds every day for the last few year with flags saying whether each day is a workday or bank holiday.
I have found lots of stuff on how to calculate the number of business days between two dates but this is more tricky.
I have created this function
ALTER function [warehouse].[MS_fnAddBusinessDays]
(#StartDate datetime,
#nDays int)
RETURNS TABLE
AS
RETURN
(SELECT calDt
FROM
(SELECT
ROW_NUMBER() OVER (ORDER BY calDt ASC) AS rownumber,
calDt
FROM
warehouse.dCalendar
WHERE
(calDt >= #StartDate)
AND (weekDayFg = 1)
AND (BankHolidayFg = 0)) AS Results
WHERE
(rownumber = #nDays)
and can call it using the following
SELECT *
FROM
(SELECT
ROW_NUMBER() OVER (ORDER BY calDt ASC) AS rownumber,
calDt, BankHolidayFg, weekDayFg, dateStr
FROM
warehouse.dCalendar
WHERE
(calDt >= CONVERT(DATETIME, '2016-12-11 00:00:00', 102))
AND (weekDayFg = 1) AND (BankHolidayFg = 0)) AS TblResults
WHERE
(rownumber = 20)
I just cannot work out how to embed this within the following example where progStartDate is the date i want to calculate the target date from
SELECT
end_user.fContactVwDn.client_no,
end_user.fProgrammeVwDn.prtyProgrammeType,
end_user.fProgrammeVwDn.progStartDate,
SUM(CASE WHEN comtContactMeetingType = 'Visit' THEN 1 ELSE 0 END) AS InitialVisitTotal,
MAX(CASE WHEN comtContactMeetingType = 'Visit' THEN contPlannedFromDate ELSE 0 END) AS InitialVisitDate
FROM
end_user.fContactVwDn
INNER JOIN
warehouse.fContactProgramme ON end_user.fContactVwDn.contKy = warehouse.fContactProgramme.contKy
INNER JOIN
end_user.fProgrammeVwDn ON warehouse.fContactProgramme.progGuid = end_user.fProgrammeVwDn.progprogGuid
GROUP BY
end_user.fProgrammeVwDn.prtyProgrammeType,
end_user.fProgrammeVwDn.progStartDate, end_user.fContactVwDn.client_no
HAVING
(end_user.fProgrammeVwDn.prtyProgrammeType = 'Application')
AND (end_user.fProgrammeVwDn.progStartDate > CONVERT(DATETIME, '2016-07-01 00:00:00', 102))
Any help would be much appreciated.

Answer 1

The function looks OK. I would add TOP, though, to avoid scanning the whole Calendar table. I hope, calDt is a primary key.
ALTER function [warehouse].[MS_fnAddBusinessDays]
(#StartDate datetime,
#nDays int)
RETURNS TABLE
AS
RETURN
(
SELECT calDt
FROM
(
SELECT TOP(#nDays)
ROW_NUMBER() OVER (ORDER BY calDt ASC) AS rownumber,
calDt
FROM
warehouse.dCalendar
WHERE
(calDt >= #StartDate)
AND (weekDayFg = 1)
AND (BankHolidayFg = 0)
ORDER BY calDt ASC
) AS Results
WHERE
rownumber = #nDays
)
This function is inline table-valued function, which means that it returns a table, not a scalar value. This is good, because scalar functions usually make queries slow, but inline (single-statement) table-valued functions can be inlined by the optimiser.
To call such function use CROSS APPLY. It was originally introduced to SQL Server specifically for calling table-valued functions, but it can do much more (it is so called lateral join).
I wrapped your original query in a CTE to make the final query readable.
WITH
CTE
AS
(
SELECT
end_user.fContactVwDn.client_no,
end_user.fProgrammeVwDn.prtyProgrammeType,
end_user.fProgrammeVwDn.progStartDate,
SUM(CASE WHEN comtContactMeetingType = 'Visit' THEN 1 ELSE 0 END) AS InitialVisitTotal,
MAX(CASE WHEN comtContactMeetingType = 'Visit' THEN contPlannedFromDate ELSE 0 END) AS InitialVisitDate
FROM
end_user.fContactVwDn
INNER JOIN warehouse.fContactProgramme ON end_user.fContactVwDn.contKy = warehouse.fContactProgramme.contKy
INNER JOIN end_user.fProgrammeVwDn ON warehouse.fContactProgramme.progGuid = end_user.fProgrammeVwDn.progprogGuid
GROUP BY
end_user.fProgrammeVwDn.prtyProgrammeType,
end_user.fProgrammeVwDn.progStartDate,
end_user.fContactVwDn.client_no
HAVING
(end_user.fProgrammeVwDn.prtyProgrammeType = 'Application')
AND (end_user.fProgrammeVwDn.progStartDate > CONVERT(DATETIME, '2016-07-01 00:00:00', 102))
)
SELECT
CTE.client_no,
CTE.prtyProgrammeType,
CTE.progStartDate,
CTE.InitialVisitTotal,
CTE.InitialVisitDate,
F.calDt
FROM
CTE
CROSS APPLY [warehouse].[MS_fnAddBusinessDays](CTE.progStartDate, 20) AS F
;