Create Incremental Count and Reset Counter for Field Change in Access

DCOUNT is extremely slow when used in a query, so I would warn you against using that technique, as is the nested subquery technique provided by Rey.

What are you using this for, is it a report or do you want to display it in a form?  If displaying it in a form, do you want the form to be editable or simply use the form to view the data?

did you try the query I posted?

storing calculated values is not advisable.

You might consider adding Dep_Num as a field in your table, and run an update query to repopulate it each time the data changes;  that way your users wouldn't have to run DCount as part of their query, and you'd avoid the potential latency mentioned by Dale.

Rey, I would ordinarily agree that storing calculation results is not a good idea.  But there are cases --like this one, where users are connecting to a data store to read static values-- where it is a good way to reduce latency.

you can always use the query to extract updated information instead of getting the info from the table.

the query  was created based on the information posted. it can be altered accordingly if there are more pertinent information provided, such  as date of birth or any historical or hierarchical information.

I actually use a function to do this, but only if I'm dumping the info into a temp table.  The function looks like:

Public Function fnRank(Reset As Boolean, ParamArray FieldValues() As Variant) As Integer

    Static myRank As Long
    Static myArray() As Variant
    Dim intLoop As Integer
    Dim bIdentical As Boolean
    
    If (Reset = True) Then
        ReDim myArray(UBound(FieldValues))
    End If
    
    bIdentical = True
    For intLoop = LBound(FieldValues) To UBound(FieldValues)
        If (bIdentical = True) And (myArray(intLoop) = FieldValues(intLoop)) Then
            'do nothing
        Else
            bIdentical = False
            myArray(intLoop) = FieldValues(intLoop)
        End If
    Next
    
    If bIdentical = False Then myRank = 0
    
    myRank = myRank + 1
    fnRank = myRank
    
End Function

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This function will run amazingly quickly (compared to the other methods mentioned above) and will accomodate as many fields as you choose to use in your ranking function.

And you would use it like:

1.  First you need to call it setting the first argument (Reset) = True and then passing in a value for each of the fields you want to use in the ranking feature.  Since the parameter array and the static array in the function are variants, you don't even need to worry about the values you pass in, just make sure you pass in a value for each column you will pass into the function in your query.  I generally call to this just before running my query.

2.  Then, you would call this as your Rank column in your query, something like the following.  In this case, we want to rank employee dependents based on their DOB, so we use an order by clause that includes both of those fields, but we only need to pass the function the EmployeeID, because we want to reset the rank  whenever the EmployeeID changes.

SELECT EmployeeID, DependentID, fnRank(0, [EmployeeID]) as Rank
FROM yourTable
Order by EmployeeID, DOB

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The down side of this technique, is that if you scroll up through the query result set, you will see that the Rank column continues to get recomputed as records move into the set of records which are visible in the query results.  So, if you scroll up, the numbers get screwed up.  To avoid this, I create a Rank table (tblRanks) and actually insert the rank values into that table, along with the unique PK value that identifies each record, something like:

currentdb.execute "DELETE * FROM tblRanks", dbfailonerror
fnRank -1, 0                                                                                                 'This resets the length of the array stored in the function
strSQL = "INSERT INTO tblRanks (PKID, Rank) " _
             & "SELECT ID, fnRank(0, [EmployeeID]) as Rank " _
             & "FROM yourTable "
             & "ORDER BY EmployeeID, DOB"
Currentdb.Execute strsql, dbfailonerror

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Then you can join tblRanks to yourTable on the PK field, something like:

SELECT EmployeeID, DependentID, R.Rank
FROM yourTable as T
INNER JOIN tblRanks as R on T.ID = R.PKID
Order by EmployeeID, DOB

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If you configure tblRanks so that the PKID field is the primary key of that table, then the query shown above should be updateable.

Sorry I didn't get a chance to post this earlier.

HTH
Dale