ACC: Functions for Calculating and Displaying Date/Time Values

ID: Q88657

The information in this article applies to:

Microsoft Access versions 1.0, 1.1, 2.0, 7.0, 97

SUMMARY

Moderate: Requires basic macro, coding, and interoperability skills.

Because a Date/Time value is stored as a double-precision number, you may receive incorrect formatting results when you try to manipulate Date/Time values in an expression. This article shows you how to create expressions and custom functions for displaying specific dates and calculating time intervals.

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access versions 1.x and 2.0. For more information about Access Basic, please refer to the "Introduction to Programming" manual in Microsoft Access version 1.x or the "Building Applications" manual in Microsoft Access version 2.0

MORE INFORMATION

Displaying Specific Dates

To display specific dates, you can use the DateSerial() function to manipulate the day, month, and year portions of a date. For example, you can use the following expressions in the ControlSource property of a text box or in the Debug window (or the Immediate window in versions 1.x and 2.0) to return specific dates:

The current month:
DateSerial(Year(Date()), Month(Date()), 1)

The next month:
DateSerial(Year(Date()), Month(Date()) + 1, 1)

The last day of the current month:
DateSerial(Year(Date()), Month(Date()) + 1, 0)

The last day of the next month:
DateSerial(Year(Date()), Month(Date()) + 2, 0)

The first day of the previous month:
DateSerial(Year(Date()), Month(Date())-1,1)

The last day of the previous month:
DateSerial(Year(Date()), Month(Date()),0)

The first day of the current quarter:
DateSerial(Year(Date()), Int((Month(Date()) - 1) / 3) * 3 + 1, 1)

The last day of the current quarter:
DateSerial(Year(Date()), Int((Month(Date()) - 1) / 3) * 3 + 4, 0)

The first day of the current week (assuming Sunday = day 1):
Date() - WeekDay(Date()) + 1

The last day of the current week:
Date() - WeekDay(Date()) + 7

The first day of the current week (using settings in Options dialog box):
Date() - WeekDay(Date(), 0) + 1

The last day of the current week:
Date() - WeekDay(Date(), 0) + 7

For information about calculating the fiscal year or fiscal month, please see the following article in the Microsoft Knowledge Base:

Q132101 ACC: How to Get the Fiscal Year/Month of a Particular Date

Calculating Time Intervals

Because a time value is stored as a fraction of a 24-hour day, you may receive incorrect formatting results when you try to add, subtract, multiply or divide time data greater than 24 hours.

For example, if you try to find the number of hours elapsed between two dates by subtracting the values in Visual Basic, you may receive an incorrect number. To demonstrate this, type the following code in the Debug window (or Immediate window in version 2.0) and note that it returns a value of 05:00 hours rather than the correct value of 53:00 hours:


   StartDate=#6/1/93 8:00AM#
   EndDate=#6/3/93 1:00PM#
   ?Format(EndDate-StartDate,"hh:mm")

To resolve formatting problems caused by time values greater than 24 hours, you can use the Int() and CSng() functions in Visual Basic to separate a calculated time value into different variables for days, hours, minutes, and seconds. For example, you can include the following code fragment in a custom function to create separate time variables:


   '-------------------------------------------------------------------
   ' This sample code separates a time interval into seven variables for
   ' the following values: days, hours, minutes, seconds, total time in
   ' hours, total time in minutes, and total time in seconds.
   '
   ' The interval argument is flexible; it can be a single value, an
   ' expression, or a field reference.
   '-------------------------------------------------------------------

   Dim totalhours As Long, totalminutes As Long, totalseconds As Long
   Dim days As Long, hours As Long, minutes As Long, seconds As Long
   Dim interval As Variant

   days = Int(CSng(interval))
   totalhours = Int(CSng(interval * 24))
   totalminutes = Int(CSng(interval * 1440))
   totalseconds = Int(CSng(interval * 86400))
   hours = totalhours Mod 24
   minutes = totalminutes Mod 60
   seconds = totalseconds Mod 60

You can use the totalhours, totalminutes, and totalseconds variables to display a time value as a single unit of time. The days, hours, minutes, and seconds variables enable you to break down a time value into portions of time. To display time values in different formats, you can concatenate these variables as demonstrated in the following sample functions:

The GetElapsedDays() function calculates the elapsed time between two date/time values and displays the result in days.

The GetElapsedTime() function calculates the elapsed time between time values and displays the result in days, hours, minutes, and seconds.

The GetTimeCardTotal() function sums a field of time values in a table and displays the total in hours and minutes.

GetElapsedDays() Sample Function

To create the GetElapsedDays() function, follow these steps:

Open the sample database Northwind.mdb.(or NWIND.MDB in versions 1.x and 2.0).

Create a module and type the following line in the Declarations section if it is not already there:
Option Explicit

Type the following function:


      Function GetElapsedDays (interval)
         Dim days As Long

         days = Int(CSng(interval))
         GetElapsedDays = days &" Days "

      End Function

To test this function, create a new query based on the Orders table.

In the QBE grid, add the following fields.

In Microsoft Access version 7.0 and 97:


         Field: ShippedDate
            Show: True
         Field: OrderDate
            Show: True
         Field: ElapsedTime: GetElapsedDays([ShippedDate]-[OrderDate])
            Show: True

In Microsoft Access versions 1.x and 2.0:


         Field: Shipped Date
            Show: True
         Field: Order Date
            Show: True
         Field: ElapsedTime: GetElapsedDays([Shipped Date]-[Order Date])
            Show: True

Run the query. Note that the ElapsedTime column displays the number of days between the ShippedDate field (or Shipped Date in versions 1.x and 2.0) and OrderDate field (or Order Date in versions 1.x and 2.0) for each record in the Orders table.

GetElapsedTime() Sample Function

To create the GetElapsedTime() function, follow these steps:

Create a new table with the following structure and save it as TimeLog.


      Table: TimeLog
      -----------------------
      Field Name: StartTime
         Data Type: Date/Time
         Format: General Date
      Field Name: EndTime
         Data Type: Date/Time
         Format: General Date

View the TimeLog table in Datasheet view, enter the following three records, and then close the table:


      StartTime                 EndTime
      --------------------------------------------
      5/10/95 4:57:00  PM       5/15/95 2:38:00 AM
      5/11/95 10:17:31 AM       5/24/95 6:05:00 PM
      5/18/95 9:16:43  AM       5/19/95 5:03:00 PM

Create a module and type the following line in the Declarations section:
Option Explicit

Enter the following function:

NOTE: In the following sample code, an underscore (_) is used as a line-continuation character. Remove the underscore from the end of the line when re-creating this code in Access Basic.


      Function GetElapsedTime (interval)
         Dim totalhours As Long, totalminutes As Long, totalseconds As _
              Long
         Dim days As Long, hours As Long, Minutes As Long, Seconds As Long

         days = Int(CSng(interval))
         totalhours = Int(CSng(interval * 24))
         totalminutes = Int(CSng(interval * 1440))
         totalseconds = Int(CSng(interval * 86400))
         hours = totalhours Mod 24
         Minutes = totalminutes Mod 60
         Seconds = totalseconds Mod 60

      GetElapsedTime = days & " Days " & hours  " Hours "  Minutes  _
         " Minutes "  Seconds  " Seconds "

      End Function

NOTE: The GetElapsedTime function requires that you pass it a date and a time.

To test this function, create a new report based on the TimeLog table using the AutoReport Wizard.

View the report in Design view.

Add an unbound text box to the TimeLog table's detail section and set its properties as follows:


      Textbox:
         Name: ElapsedTime
         ControlSource: =GetElapsedTime([EndTime]-[StartTime])
         Width: 3 inches

Preview the report. Note that each record displays the total elapsed time in days, hours, minutes, and seconds.

GetTimeCardTotal() Sample Function

To create the GetTimeCardTotal() function, follow these steps:

Create a new table with the following structure and save it as TimeCard.


      Table: TimeCard
      -----------------------
      Field Name: Daily Hours
         Data Type: Date/Time
         Format: Short Time

View the TimeCard table in Datasheet view, enter the following four records, and then close the table:
8:15
7:37
8:12
8:03

Create a module and type the following line in the Declarations section if it's not already there:
Option Explicit

Type the following function:


      Function GetTimeCardTotal ()
         Dim db As Database, rs As Recordset
         Dim totalhours As Long, totalminutes As Long
         Dim days As Long, hours As Long, minutes As Long
         Dim interval As Variant, j As Integer

         Set db = dbengine.workspaces(0).databases(0)
         Set rs = db.OpenRecordset("timecard")
         interval = #12:00:00 AM#
            While Not rs.EOF
               interval = interval + rs![Daily hours]
               rs.MoveNext
            Wend
         totalhours = Int(CSng(interval * 24))
         totalminutes = Int(CSng(interval * 1440))
         hours = totalhours Mod 24
         minutes = totalminutes Mod 60

      GetTimeCardTotal = totalhours &" hours and " &minutes &" minutes"

      End Function

To test this function, type the following line in the Debug window (or Immediate window in version 1.x and 2.0), and then press ENTER:
? GetTimeCardTotal ()
Note that the Debug window displays 32 hours and 7 minutes.

REFERENCES

For more information about calculating date/time values, please see the following article in the Microsoft Knowledge Base:

Q130514 ACC: Storing, Calculating, and Comparing Date/Time Data

Additional query words: fractional

Keywords : kbprg
Version : WINDOWS:1.0,1.1,2.0,7.0,97
Platform : WINDOWS
Issue type : kbhowto