Public Sub CreateField()
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    Dim blnFieldExists As Boolean
    
    Set db = OpenDatabase("D:\1\internet.mdb")
    Set tdf = db.TableDefs("Report")
    
    For Each fld In tdf.Fields
        If fld.Name = "N" Then
            Exit For
            blnFieldExists = True
        End If
    Next fld
    
    If Not blnFieldExists Then
        With tdf
            .Fields.Append .CreateField("N", dbText)
        End With
    End If
    
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Sub

        With tdf
            .Fields.Append .CreateField("N", dbInteger)
            '.Fields.Append .CreateField("N", dbLong)
        End With

Public Sub CreateFieldADO()
    Dim cnn As ADODB.Connection
    
    Set cnn = New ADODB.Connection
    
    cnn.Open "Provider=Microsoft.Jet.OLEDB.4.0;" & _
      "Data Source=D:\1\internet.mdb;Persist Security Info=False"
      
    cnn.Execute "ALTER TABLE Report " _
      & "ADD COLUMN N NUMERIC(18,3)"
    
    cnn.Close
    
    Set cnn = Nothing
End Sub

Public Sub CreateFieldDAO()
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    Dim prp As DAO.Property
    Dim blnFieldExists As Boolean
    
    Set db = OpenDatabase("D:\1\internet.mdb")
    Set tdf = db.TableDefs("Report")
    
    For Each fld In tdf.Fields
        If fld.Name = "N" Then
            Exit For
            blnFieldExists = True
        End If
    Next fld
    
    If Not blnFieldExists Then
        Set fld = tdf.CreateField("N", dbBigInt)
        tdf.Fields.Append fld
        
        db.TableDefs.Refresh

        Set prp = fld.CreateProperty("Precision",  2 ,  18 )
        fld.Properties.Append prp

        Set prp = fld.CreateProperty("Scale",  2 ,  3 )
        fld.Properties.Append prp
    End If
    
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Sub