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Overlapping Date Ranges
PAUG – Tips & Tricks
September 2002
Sam Gray
Misc Comments
Don’t take notes! This talk will be available online (slides and code)– PAUG website (eventually, maybe)– My website:
http://timestream.net/PAUG Questions, comments, corrections, additions:
[email protected] I’m looking for work!
http://timestream.net/resume
Why Check For Overlaps?
Because they shouldn’t be there whenever only one thing can happen during a given time:– Scheduling application (classes, meeting rooms,
any limited resource)9/27 8:00 am 9/27 12:00 pm Intro to VB
9/27 1:00 pm 9/27 5:00 pm Advanced VB
– Billing applications (various rates applied over time), e.g., health insurance costs:
1/1/2001 12/31/2001 $200/month
1/1/2002 12/31/2002 $300/month
How Do You Find Them?
My first attempt 3 years ago was extremely messy (18 lines of WHERE criteria!) and complex (and only worked for one table).
Revisited problem recently. First mapped all possible relationships between date ranges.
Then constructed WHERE criteria to catch the conflicts.
Date Range Conflicts
Contiguous (?)Partial overlap (2)Inside (3)OutsideIdenticalSame Start/End
Contiguous Ranges (Special Case)
Contiguous: “touching along a boundary.” One period starts at the exact same time another ends.
Generally OK for: Scheduling rooms, classes, etc – when working with times.
Not OK for: Most financial applications – when working with days.
9/27/2001 11:30 am
These Four Query Criteria Should Find All Conflicts
StartDate, StopDate: Field names in table
Begin, End: New values being tested for conflicts
1. StartDate < Begin AND StopDate > BeginPartial Overlap 1, Inside 1, Inside 3
2. StartDate < End AND StopDate > EndPartial Overlap 2, Inside 1, Inside 2
3. StartDate > Begin AND StopDate < EndOutside
4. StartDate = Begin OR EndDate = EndIdentical, Same Start, Same End
Note: If contiguous ranges not OK, change < to <= and > to >=.
Leads to... Generalized Procedure
Ugly function call, but extremely reusable:Public Function DateRangesOverlap( _ sTableName As String, _ sStartFieldName As String, dtStartDate As Date, _ sEndFieldName As String, dtEndDate As Date, _ sIDFieldName As String, _ Optional lngIDValueToExclude As Long, _ Optional bAllowContiguousRanges As Boolean = True, _ Optional sOtherCriteria As String, _ Optional rsIDs As ADODB.Recordset) As Long
[~100 lines of code]
End Function
