MS Access 2019：无法使用 VBA 中的 SQL 查询填充表单字段

Question

I want to auto-populate a field in my form based on the results of an SQL query. I'm just not sure of the proper syntax to get it to properly read the query. This is what I've got, but it's not returning the value of the query, it's actually just returning the text of the query itself.

Private Sub PurchBatchNo_Enter()

Dim MostRecentPurchBatch As String
MostRecentPurchBatch = "SELECT Max(PurchaseBatchNo) FROM purchases"
Me.PurchBatchNo.Value = MostRecentPurchBatch

End Sub

I'm sure the issue has to do with the quotation marks, but it doesn't work without them either, and I'm not sure how to write it properly.

Thanks for being here for beginners like me!

Answer 1

All your code does is set a variable to a string of characters then attempts to set value of field with that string.

But why would you want to populate field with a value already used in a record? Most likely you need to increment by 1.

To use an SQL statement, would have to open a recordset object then reference field of recordset.

Private Sub PurchBatchNo_Enter()
Dim MostRecentPurchBatch As DAO.Recordset
If IsNull(Me.PurchBatchNo) Then
    Set MostRecentPurchBatch = CurrentDb.OpenRecordset("SELECT Max(PurchaseBatchNo) AS MaxBatch FROM purchases")
    Me.PurchBatchNo = MostRecentPurchBatch!MaxBatch + 1
End If
End Sub

However, pulling a single value from table is what domain aggregate functions are good for.

Private Sub PurchBatchNo_Enter()
If IsNull(Me.PurchBatchNo) Then Me.PurchBatchNo = DMax("PurchaseBatchNo", "purchases") + 1
End Sub

Instead of using VBA procedure, consider just setting DefaultValue property of textbox bound to PurchBatchNo field with the DMax() expression. As soon as record is initiated by input to another textbox, the PurchBatchNo will populate.

If user should not be able to edit this value, set textbox as Locked Yes and TabStop No and use a different event for the VBA code if you go with VBA.