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HowTo: Calculate business days - pure SQL approach.

FishVal
Expert 2.5K+
P: 2,653
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]
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  1. SELECT DateSerial(tblYears.lngYear,tblMonths.lngMonth,tblDays.lngDay) AS dteDate,
  2. tblYears.lngYear, tblMonths.lngMonth, tblDays.lngDay
  3. FROM tblYears, tblMonths, tblDays
  4. WHERE tblDays.lngDay=Day(DateSerial([tblYears].[lngYear],[tblMonths].[lngMonth],[tblDays].[lngDay]));
  5.  
Then, outer join with [tblPeriods]:

Query: [qryContactsPeriodsDays]
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  1. SELECT qryFlatCalendar.*, tblPeriods.keyPeriodID, tblPeriods.keyContactID, tblPeriods.dteStart, tblPeriods.dteEnd
  2. FROM qryFlatCalendar LEFT JOIN tblPeriods ON (tblPeriods.dteStart<=qryFlatCalendar.dteDate) AND (tblPeriods.dteEnd>=qryFlatCalendar.dteDate)
  3. WHERE Not tblPeriods.keyContactID Is Null;
  4.  
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]
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  1. SELECT tblContacts.*, tblCountryDaysOff.lngContactDayOff
  2. FROM tblContacts INNER JOIN tblCountryDaysOff
  3. ON tblContacts.keyCountryID = tblCountryDaysOff.keyCountryID;
  4.  
Query: [qryContactsHolidaysDates]
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  1. SELECT tblContacts.*, tblCountryHolidays.keyCountryHolidayID, 
  2. tblCountryHolidays.txtHolidayName, tblHolydayDates.keyHolidayID, tblHolydayDates.lngDay, tblHolydayDates.lngMonth, tblHolydayDates.lngYear
  3. FROM (tblContacts INNER JOIN tblCountryHolidays
  4. ON tblContacts.keyCountryID = tblCountryHolidays.keyCountryID)
  5. INNER JOIN tblHolydayDates
  6. ON tblCountryHolidays.keyCountryHolidayID=tblHolydayDates.keyCountryHolidayID;
  7.  
First we will exclude days off via the following outer join:

Query: [qryContactsPeriodsDaysWODaysOff]
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  1. SELECT qryContactsPeriodsDays.*, qryContactsDaysOff.lngContactDayOff
  2. FROM qryContactsPeriodsDays
  3. LEFT JOIN qryContactsDaysOff
  4. ON 
  5. (qryContactsPeriodsDays.keyContactID=qryContactsDaysOff.keyContactID) AND (WeekDay(qryContactsPeriodsDays.dteDate)=qryContactsDaysOff.lngContactDayOff)
  6. WHERE qryContactsDaysOff.lngContactDayOff Is Null;
  7.  
Next we will exclude holidays:

Query: [qryContactsPeriodsBusinessDays]
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  1. SELECT qryContactsPeriodsDaysWODaysOff.keyPeriodID, 
  2. qryContactsPeriodsDaysWODaysOff.keyContactID, qryContactsPeriodsDaysWODaysOff.dteDate, 
  3. qryContactsHolidaysDates.txtHolidayName
  4. FROM qryContactsPeriodsDaysWODaysOff
  5. LEFT JOIN qryContactsHolidaysDates
  6. ON 
  7. (qryContactsPeriodsDaysWODaysOff.lngYear=qryContactsHolidaysDates.lngYear Or qryContactsHolidaysDates.lngYear Is Null)
  8. AND (qryContactsPeriodsDaysWODaysOff.lngMonth=qryContactsHolidaysDates.lngMonth) AND 
  9. (qryContactsPeriodsDaysWODaysOff.lngDay=qryContactsHolidaysDates.lngDay) AND 
  10. (qryContactsPeriodsDaysWODaysOff.keyContactID=qryContactsHolidaysDates.keyContactID)
  11. WHERE qryContactsHolidaysDates.keyCountryHolidayID Is Null;
  12.  


Step 3. Counting days.

Now dessert.

Query: [qryContactsPeroidsBusinessDaysCounts]
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  1. SELECT qryContactsPeriodsBusinessDays.keyPeriodID, 
  2. qryContactsPeriodsBusinessDays.keyContactID,
  3. Count(qryContactsPeriodsBusinessDays.dteDate) 
  4. AS CountOfdteDate
  5. FROM qryContactsPeriodsBusinessDays
  6. GROUP BY qryContactsPeriodsBusinessDays.keyPeriodID, 
  7. qryContactsPeriodsBusinessDays.keyContactID;
  8.  
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]
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  1. SELECT tblPeriods.*, Nz(qryContactsPeroidsBusinessDaysCounts.CountOfdteDate,0) AS 
  2. lngBusinessDays
  3. FROM tblPeriods
  4. LEFT JOIN qryContactsPeroidsBusinessDaysCounts
  5. ON tblPeriods.keyPeriodID=qryContactsPeroidsBusinessDaysCounts.keyPeriodID;
  6.  
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.
Nov 27 '08 #1
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5 Comments


FishVal
Expert 2.5K+
P: 2,653
Ok. Here is a sample.
Attached Files
File Type: zip Calendar.zip (42.3 KB, 656 views)
Nov 30 '08 #2

100+
P: 675
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."
Dec 5 '08 #3

FishVal
Expert 2.5K+
P: 2,653
Amen. :)

Thanks.
Dec 5 '08 #4

P: 2
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
Jul 29 '09 #5

P: 31
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..
Aug 2 '09 #6

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