如何确定有多少人登陆数据库？

Sub ShowUserRosterMultipleUsers()
    Dim cn As New ADODB.Connection
    Dim cn2 As New ADODB.Connection
    Dim rs As New ADODB.Recordset
    Dim i, j As Long
    cn.Provider = "Microsoft.Jet.OLEDB.4.0"
    cn.Open "Data Source=c:\Northwind.mdb"
    cn2.Open "Provider=Microsoft.Jet.OLEDB.4.0;" _