HowTo: Calculate business days - pure SQL approach.

[FishVal]

IMHO, the following is not a how-to-do instruction to solve a particular problem but more a concept-proof stuff demonstrating possibilities of SQL.

So, let us say the problem is to calculate business days count which is defined as count of days (optionally inclusive in the current implementation) excluding weekend days and holidays.

Let us say periods to calculate are stored in table associated with contacts.

[tblPeriods]
keyPeriodID - Autonumber(Long), PK
keyContactID - Long, FK(tblContacts)
dteStart - Date/Time
dteEnd - Date/Time

The goal is to receive dataset containing sequential dates falling into date periods stored in the table with weekends and holidays excluded. Then, a simple grouping query will return desired results.


Step 1. Getting records.

To get all days falling into the periods we need to outer join [tblPeriods] with dataset containing all sequential dates.
Obviously using a table storing all dates is not a smart option. ;)
Better to generate it dynamically.
Obviously calendar dates are nothing more than all possible combinations of 1-31 days numbers, 1-12 month numbers and sensible range of year numbers. Certainly non-existing dates like 30-Dec and sometimes 29-Dec has to be omitted.
This gives an idea to use cartesian join of the following datasets:

[tblDays]
lngDay - Long, PK - natural numbers set 1-31

[tblMonts]
lngMonth - Long, PK - natural numbers set 1-12

[tblYears]
lngYear - Long, PK - natural numbers set ... :) ... let us say 2000 - 2014

The following query will combine these values into flat calendar 2000-2014, non existing dates are excluded using a feature of DateSerial() function to wrap day in a case of illegal argumnets.

Query: [qryFlatCalendar]

SELECT DateSerial(tblYears.lngYear,tblMonths.lngMonth,tblDays.lngDay) AS dteDate,
tblYears.lngYear, tblMonths.lngMonth, tblDays.lngDay
FROM tblYears, tblMonths, tblDays
WHERE tblDays.lngDay=Day(DateSerial([tblYears].[lngYear],[tblMonths].[lngMonth],[tblDays].[lngDay]));
 

Then, outer join with [tblPeriods]:

Query: [qryContactsPeriodsDays]

SELECT qryFlatCalendar.*, tblPeriods.keyPeriodID, tblPeriods.keyContactID, tblPeriods.dteStart, tblPeriods.dteEnd
FROM qryFlatCalendar LEFT JOIN tblPeriods ON (tblPeriods.dteStart<=qryFlatCalendar.dteDate) AND (tblPeriods.dteEnd>=qryFlatCalendar.dteDate)
WHERE Not tblPeriods.keyContactID Is Null;
 

Pay attention to the ON clause of the query. In current implementation both sides of period are inclusive. If you consider other logic, then it is the place where it should be implemented.



Step 2. Excluding weekends and holidays.

Now we are going to exclude weekend days off and holidays.
And immediately appear two issues - as usual one is easy and other not so :)

• Weekend days off depend on particular country.
• Holidays sets depend on country too. The problem is that in some cases holiday date is the same in each year, in some cases it is calculated using some rules which not always could be easily embedded into relational database. So, for simplicity, let us store explicit full dates of that "irregular" holidays while "regular" holydays don't require more than a single record with Null year value.

Obviously days sets to exlude (weekends and holidays) when calculating business days should be associated with a particular country. As well as contacts.

This requires several tables:

[tblCountries]
keyCountryID - Autonumber(Long), PK
txtCountry - Text

[tblCountryDaysOff]
keyContactDayOffID - Autonumber(Long), PK
keyCountryID - Long, FK(tblCountries)
lngContactDayOff - Long

[tblCountryHolidays]
keyCountryHolidayID - Autonumber(Long), PK
keyCountryID - Long, FK(tblCountries)
txtHolidayName - Text

[tblContacts]
keyContactID - Autonumber(Long), PK
keyCountryID - Long, FK(tblCountries)
txtContactName - Text

* the following table associates holidays with dates, if holiday occurs in definite day of month each year, then a single record is used with [lngYear]=Null, otherwise record for each year has to be created

[tblHolydayDates]
keyHolidayID - Autonumber(Long), PK
lngDay- long
lngMonth - Long
lngYear - Long
keyCountryHolidayID - Long, FK(tblCountryHolidays)

Now two prejoins to get associations - Contact/DaysOff, Contact/HolidayDate

Query: [qryContactsDaysOff]

SELECT tblContacts.*, tblCountryDaysOff.lngContactDayOff
FROM tblContacts INNER JOIN tblCountryDaysOff
ON tblContacts.keyCountryID = tblCountryDaysOff.keyCountryID;
 

Query: [qryContactsHolidaysDates]

SELECT tblContacts.*, tblCountryHolidays.keyCountryHolidayID, 
tblCountryHolidays.txtHolidayName, tblHolydayDates.keyHolidayID, tblHolydayDates.lngDay, tblHolydayDates.lngMonth, tblHolydayDates.lngYear
FROM (tblContacts INNER JOIN tblCountryHolidays
ON tblContacts.keyCountryID = tblCountryHolidays.keyCountryID)
INNER JOIN tblHolydayDates
ON tblCountryHolidays.keyCountryHolidayID=tblHolydayDates.keyCountryHolidayID;
 

First we will exclude days off via the following outer join:

Query: [qryContactsPeriodsDaysWODaysOff]

SELECT qryContactsPeriodsDays.*, qryContactsDaysOff.lngContactDayOff
FROM qryContactsPeriodsDays
LEFT JOIN qryContactsDaysOff
ON 
(qryContactsPeriodsDays.keyContactID=qryContactsDaysOff.keyContactID) AND (WeekDay(qryContactsPeriodsDays.dteDate)=qryContactsDaysOff.lngContactDayOff)
WHERE qryContactsDaysOff.lngContactDayOff Is Null;
 

Next we will exclude holidays:

Query: [qryContactsPeriodsBusinessDays]

SELECT qryContactsPeriodsDaysWODaysOff.keyPeriodID, 
qryContactsPeriodsDaysWODaysOff.keyContactID, qryContactsPeriodsDaysWODaysOff.dteDate, 
qryContactsHolidaysDates.txtHolidayName
FROM qryContactsPeriodsDaysWODaysOff
LEFT JOIN qryContactsHolidaysDates
ON 
(qryContactsPeriodsDaysWODaysOff.lngYear=qryContactsHolidaysDates.lngYear Or qryContactsHolidaysDates.lngYear Is Null)
AND (qryContactsPeriodsDaysWODaysOff.lngMonth=qryContactsHolidaysDates.lngMonth) AND 
(qryContactsPeriodsDaysWODaysOff.lngDay=qryContactsHolidaysDates.lngDay) AND 
(qryContactsPeriodsDaysWODaysOff.keyContactID=qryContactsHolidaysDates.keyContactID)
WHERE qryContactsHolidaysDates.keyCountryHolidayID Is Null;
 

Step 3. Counting days.

Now dessert.

Query: [qryContactsPeroidsBusinessDaysCounts]

SELECT qryContactsPeriodsBusinessDays.keyPeriodID, 
qryContactsPeriodsBusinessDays.keyContactID,
Count(qryContactsPeriodsBusinessDays.dteDate) 
AS CountOfdteDate
FROM qryContactsPeriodsBusinessDays
GROUP BY qryContactsPeriodsBusinessDays.keyPeriodID, 
qryContactsPeriodsBusinessDays.keyContactID;
 

Well. Almost done.
However periods having zero count of business days do not appear in the resulting list.

So, let Uroboros bite his tail.

Query: [qryFinalJoin]

SELECT tblPeriods.*, Nz(qryContactsPeroidsBusinessDaysCounts.CountOfdteDate,0) AS 
lngBusinessDays
FROM tblPeriods
LEFT JOIN qryContactsPeroidsBusinessDaysCounts
ON tblPeriods.keyPeriodID=qryContactsPeroidsBusinessDaysCounts.keyPeriodID;
 

P.S. Holidays list in the attached database could be incomplete, wrong or irrelevant. I didn't try my best to make a good one. :D

P.P.S. Ok. No sample today because the maximum allowed size was 5k. :D Just another bug in current state of bytes.com.

[FishVal]

Ok. Here is a sample.

[OldBirdman]

The sentence "Certainly non-existing dates like 30-Dec and sometimes 29-Dec has to be omitted." should replace Dec with Feb. Or maybe "Certainly the non-existing dates 31-Apr, 31-June, 31-Sep, 31-Nov, 31-Feb, 31-Feb and sometimes 29-Feb have to be omitted."

[FishVal]

Amen. :)

Thanks.

[chevyas123]

How do i write a function to calculate business days excluding weekends and holidays in oracle?
Actually i need to prepare a calendar for my monthly activities i.e activity x to be performed on 3rd workingday of month.
Can u please help me out with this as i am very new to oracle.
Plzzzzzzz

[totomalas]

thanks alot for this amazing work....I have had this problem for so long...I want to get all the records that are between... Todays Date and the first day of this year....

what i do now is this..

Between Date() and [ I let the user enter the 1st day of the year, e.g 1/1/2009]



I couldnt figure it out... please help..