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大神帮忙看下，代码出错了，怎么改

Select Case e.DataCol.Name

Case "上次欠款","上货金额","退货金额","还款金额","欠款金额"

Dim dr As DataRow

Dim drs As List(of DataRow)

dr = e.DataTable.Find("[_SortKey] < " & e.DataRow("_SortKey"), "[_SortKey] Desc")

If dr Is Nothing Then

e.DataRow("欠款余额") = e.DataRow("上次欠款") + e.DataRow("上货金额")-e.DataRow("退货金额")- e.DataRow("还款金额")

dr = e.DataRow

End If

drs = e.DataTable.Select("[_SortKey] >= " & dr("_SortKey"), "[_SortKey]")

For i As Integer = 1 To drs.Count - 1

drs(i)("欠款余额") = drs(i-1)("上次欠款") + drs(i)("上货金额") - drs(i)("退货金额") - drs(i)("还款金额")

End Select