Select Case MainTable.name

    Case "材料收支明细账"
        Dim rq As Date = Date.Today
        Dim y As Integer = rq.Year
        Dim m As Integer = rq.Month
        Dim drs As List(of DataRow)
        Dim rqstr As String = Format(rq,"yyyyMM")
        DataTables("材料收支明细账").DeleteFor("凭证号 like \'R" & rqstr & "*\' or 凭证号 like \'C" & rqstr & "*\'")
        DataTables("材料收支明细账").Save()
        Dim pr1s As List(of DataRow) = DataTables("采购入库单").Select("入库单号 like \'R" & rqstr & "*\'","到货日期")
        Dim pr2s As List(of DataRow) = DataTables("材料出库单").Select("出库单号 like \'C" & rqstr & "*\'","领料日期")
        ...

End Select

代码如上，橙色字体部分，pr1s和pr2s用Dim prs As List(of DataRow) = pr1s. AddRange(pr2s)不能按日期排序。

用什么方法将pr1s和pr2s合并后按日期排序？（日期相同的将采购入库单排在前面）