Generate a sequential number (per group) when adding a row to an Access table

Question

I have an MS Access (.accdb) table with data like the following:

Location Number
-------- ------
ABC      1
DEF              


        

Answer 1

For Access 2010 and newer, this is a better way to do it. It uses the table's Before Change Data Macro to derive the next sequential number and put it in the [Number] field of the new record:

The advantages of this approach are:

• The sequence number will be applied whenever a new record is added, regardless of how it is added.
• The Excel VBA code does not have to worry about creating the sequence number; it "just happens".
• Since this code resides at the table level it should be safe for a multi-user environment.

For more information on Data Macros, see

Create a data macro

Answer 2

You need to add a new column to your table of data type AutoNumber.

office.microsoft.com: Fields that generate numbers automatically in Access

You should probably also set this column as your primary key.

Answer 3

I suspect that you are looking for something like this:

Dim con As ADODB.Connection, cmd As ADODB.Command, rst As ADODB.Recordset
Dim newNum As Variant

Const fLabel_Location = "O'Hare"  ' test data

Set con = New ADODB.Connection
con.Open "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\Public\Database1.accdb;"

Set cmd = New ADODB.Command
cmd.ActiveConnection = con
cmd.CommandText = "SELECT MAX(Number) AS maxNum FROM Articles WHERE Location = ?"
cmd.CreateParameter "?", adVarWChar, adParamInput, 255
cmd.Parameters(0).Value = fLabel_Location
Set rst = cmd.Execute
newNum = IIf(IsNull(rst("maxNum").Value), 0, rst("maxNum").Value) + 1
rst.Close

rst.Open "Articles", con, adOpenDynamic, adLockOptimistic, adCmdTable
rst.AddNew
rst("Location").Value = fLabel_Location
rst("Number").Value = newNum
rst.Update
rst.Close
Set rst = Nothing
Set cmd = Nothing
con.Close
Set con = Nothing

Note, however, that this code is not multiuser-safe. If there is the possibility of more than one user running this code at the same time then you could wind up with duplicate [Number] values.

(To make the code multiuser-safe you would need to create a unique index on ([Location], [Number]) and add some error trapping in case the rst.Update fails.)

Edit

For Access 2010 and later consider using an event-driven Data Macro and shown in my other answer to this question.