DAO查询中计算累计余额

请各位老师能帮助下吗，谢谢！

我想写个动态余额累计函数，适用于不同的数据源，只管调用即可。这是我的原码：

Function ljuy(bmc As String, fzzd As String, lsh As Double, jf As Double, df As Double) As Double
'bmc：表名称 _
  fzzd：分组字段 _
  lsh：序号字段 _
  jf：借方 _
  df：贷方 _
  调用：ljuy("表名称","分组字段名称",[序号排序字段名称],[借方字段名称],[贷方字段名称])
    On Error GoTo Err
    Dim rst As Object
    Dim ye As Double
    Dim a As String
    Dim strSQL As String
    strSQL = "SELECT * FROM [往来单据] ORDER BY 往来代码,顺序号"
    Set rst = CurrentDb.OpenRecordset(strSQL, dbOpenDynaset)
    rst.MoveFirst


    a = rst!往来代码
    Do Until rst.EOF = True
        If a <> rst!往来代码 Then
            a = rst!往来代码
            ye = 0
        End If
        If lsh = rst!顺序号 Then
            ye = ye + Nz(rst!借方金额) - Nz(rst!贷方金额)
            ljuy = ye
            Exit Do
        ElseIf lsh <> rst!顺序号 Then
            ye = ye + Nz(rst!借方金额) - Nz(rst!贷方金额)
        End If
        rst.MoveNext
    Loop
    rst.Close
    Set rst = Nothing


Exit_ERR:
    Exit Function


Err:
    MsgBox Err.Description
    Resume Exit_ERR
End Function

请老师们能帮忙修改吗，谢谢！！