合计数不正确

SQL视图上粘贴以下代码：

SELECT DISTINCTROW 总表.厂商编码, 总表.品牌, Sum(确认表.金额) AS 确认表金额合计, Sum(抵租表.金额) AS 抵租表金额合计, Nz([确认表金额合计])-Nz([抵租表金额合计]) AS 余额
FROM (总表 LEFT JOIN 确认表 ON 总表.[厂商编码] = 确认表.[厂商编码]) LEFT JOIN 抵租表 ON 总表.[厂商编码] = 抵租表.[厂商编码]
GROUP BY 总表.厂商编码, 总表.品牌;