bd2.Totals.AddExp("最终结算金额","iif(批准金额 is null, 0, 批准金额) - iif(业主扣款金额 is null, 0, 业主扣款金额) - iif(总包扣款金额 is null, 0, 总包扣款金额) - iif(其他扣款金额 is null, 0, 其他扣款金额)","结算金额(元)")