在ACCESS VBA中，当进行表格操作时，可能会出现重复输入数据的问题。为避免这种情况的发生，可以通过以下代码示例进行处理：

1. 使用DAO对象打开表格并进行查找

Dim db As DAO.Database
Dim rs As DAO.Recordset
Dim strSQL As String
Set db = CurrentDb
strSQL = "SELECT [FieldName] FROM [TableName] WHERE [FieldName]='" & Me.FieldName & "'"
Set rs = db.OpenRecordset(strSQL)
If rs.RecordCount > 0 Then
    MsgBox "该条记录已经存在.", vbExclamation, "重复数据"
    Me.Undo
    Exit Sub
End If

2. 利用querydef对象执行SQL语句进行查找

Dim qd As DAO.QueryDef
Dim db As DAO.Database
Dim strSQL As String
Dim prm As DAO.Parameter
 
Set db = CurrentDb
Set qd = db.CreateQueryDef("")
 
strSQL = "SELECT [FieldName] FROM [TableName] WHERE [FieldName]='" & Me.FieldName & "'"
 
With qd
    .SQL = strSQL
    For Each prm In .Parameters
        prm.Visible = False
    Next prm
    Set rs = .OpenRecordset(dbOpenSnapshot)
End With
 
If Not rs.EOF Then
    MsgBox "该条记录已经存在.", vbExclamation, "重复数据"
    Me.Undo
    Exit Sub
End If
 
rs.Close
Set rs = Nothing
Set qd = Nothing
Set db = Nothing

以上两种方法都可以避免在表格中出现重复数据的情况，并且可以按需选择适用于自己的代码。