主题：[求助]表达式的统计列

Dim a As New SQLGroupTableBuilder("应收款列表","chargeslist")

a.C

a.AddTable("chargeslist","taskno","task_list","taskno") '添加统计表

a.Groups.AddDef("{chargeslist}.taskno","任务编码") '根据产品名称分组

a.Groups.AddDef("studentno","学生编码")

a.Totals.AddDef("shishou","实收") '对数量进行统计

a.Totals.AddExp("yingfu","yingshou - shishou","未收款")

a.filter="{task_list}.taskstatus='收支' and (typeofrec='收费开单' or typeofrec='收费')"

Tables("费用收支_Table1").DataSource = a.BuildDataSource()

开单有数据，实收有数据，未收款无数据，那里设置出错了？

关键：a.Totals.AddExp("yingfu","isnull([yingshou],0) - isnull([shishou],0)","未收款")