主题：组合统计出错

Dim a As New GroupTableBuilder("入库表1",DataTables("电机壳生产明细")) Dim a1 As fxDataSource a.Groups.AddDef("规格") a.Groups.AddDef("物料编码") a.Groups.AddDef("入库工序","工序") a.Totals.AddDef("入库数量","入库_数量") a1 = a.BuildDataSource() Dim b As New GroupTableBuilder("领用表1",DataTables("电机壳生产明细")) Dim b1 As fxDataSource b.Groups.AddDef("规格") b.Groups.AddDef("物料编码") b.Groups.AddDef("领用工序","工序") b.Totals.AddDef("领用数量","领用_数量") b1 = b.BuildDataSource() Dim c As New GroupTableBuilder("出库表1",DataTables("出库明细表")) Dim c1 As fxDataSource c.Groups.AddDef("规格") c.Groups.AddDef("物料编码") c.Groups.AddDef("工序") c.Totals.AddDef("数量","出库_数量") c1 = c.BuildDataSource() Dim d As New GroupTableBuilder("结存表1",DataTables("结存表")) Dim d1 As fxDataSource d.Groups.AddDef("规格") d.Groups.AddDef("物料编码") d.Groups.AddDef("工序") d.Totals.AddDef("上期结存","结存_数量") d1 = d.BuildDataSource() Dim nms As String()={"规格", "物料编码", "工序"} a1.Combine(nms, d1,nms) b1.Combine(nms, d1,nms) c1.Combine(nms, d1,nms) Tables("窗口1_Table1").DataSource = d1 '将统计结果绑定到Table With DataTables("窗口1_Table1").DataCols '用表达式列计算库存数据 .Add("库存_数量",Gettype(Integer), "IsNull([结存_数量],0) + ISNULL([入库_数量],0) - ISNULL([领用_数量],0) - ISNULL([出库_数量],0) ") End With 这段代码中，最后显示是说，1.找不到入库数量 2.结存表中不存在库存_数量多列 不懂是为什么？