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Dim bd1 As New GroupTableBuilder("统计表1",DataTables("销售记录表"))

Dim dt1 As fxDataSource

bd1.Groups.AddDef("订单编号")

bd1.Totals.AddDef("眼镜报价")

bd1.Totals.AddDef("衣服报价")

bd1.Totals.AddDef("裤子报价")

bd1.Filter = "订单编号 is not null"

dt1 = bd1.BuildDataSource()

Dim bd2 As New SQLGroupTableBuilder("统计表2",("眼镜采购表"))

Dim dt2 As fxDataSource

bd2.Groups.AddDef("订单编号")

bd2.Totals.AddExp("眼镜成本","眼镜框成本 + 眼镜片成本 + 眼镜盒成本")

bd2.Filter = "订单编号 is not null"

dt2 = bd2.BuildDataSource()

Dim bd3 As New SQLGroupTableBuilder("统计表3",("衣服采购成本"))

Dim dt3 As fxDataSource

bd3.Groups.AddDef("订单编号")

bd3.Totals.AddExp("衣服成本","面料成本 + 设计成本")

bd3.Filter = "订单编号 is not null"

dt3 = bd3.BuildDataSource()

Dim bd4 As New SQLGroupTableBuilder("统计表4",("裤子采购成本"))

Dim dt4 As fxDataSource

bd4.Groups.AddDef("订单编号")

bd4.Totals.AddExp("裤子成本","仓库成本 + 破损成本")

bd4.Filter = "订单编号 is not null"

dt4 = bd4.BuildDataSource()

dt1.Combine("订单编号",dt2,"订单编号") '将销售统计数据组合到进货统计数据

dt1.Combine("订单编号",dt3,"订单编号") '将退货统计数据组合到进货统计数据

dt1.Combine("订单编号",dt4,"订单编号") '将退货统计数据组合到进货统计数据

dt1.Show("统计表1")

With DataTables("统计表1").DataCols '用表达式列计算库存数据

.Add("利润",Gettype(Double), "IsNull([眼镜报价],0) + ISNULL([衣服报价],0) + ISNULL([裤子报价],0) - ISNULL([眼镜成本],0) - ISNULL([衣服成本],0) - ISNULL([裤子成本],0)")

End With

主题：老师如何实现跨表计算？