我把两个数据库由等值连接换成右连接，怎么系统（PB+sql做的系统中自定义报表）会报错？如图所示
能告诉我等值连接，左连接，右连接的区别吗？有什么需要注意的？谢谢！

语句贴出来

SELECT
RS_Dorm.DormNo,
RS_DormWaterElec.WaterPrice,
RS_DormWaterElec.ElecPrice,
RS_Dorm.BuildingNo,
RS_DormWaterElec.ElecFee,
RS_DormMonthFee.FeeMonth,
RS_Emp.EmpNo,
RS_DormWaterElec.WaterFee
FROM
RS_Dorm,
RS_DormWaterElec,
RS_DormMonthFee,
RS_Emp
WHERE
RS_Dorm.DormSysID = RS_DormWaterElec.DormSysID And
RS_DormMonthFee.FeeMonth = convert(varchar(7),RS_DormWaterElec.ReadMonth,121) And
RS_DormMonthFee.DormSysID *= RS_DormWaterElec.DormSysID And
RS_DormMonthFee.EmpSysID = RS_Emp.EmpSysID
ORDER BY
RS_Dorm.DormNo ASC

                RS_DormMonthFee.FeeMonth  *=  convert(varchar(7),RS_DormWaterElec.ReadMonth,121)  And

不行啊，还是报错

SELECT
RS_Dorm.DormNo,
RS_DormWaterElec.WaterPrice,
RS_DormWaterElec.ElecPrice,
RS_Dorm.BuildingNo,
RS_DormWaterElec.ElecFee,
RS_DormMonthFee.FeeMonth,
RS_Emp.EmpNo,
RS_DormWaterElec.WaterFee
FROM
RS_Dorm,
RS_DormWaterElec,
RS_DormMonthFee,
RS_Emp
WHERE
RS_Dorm.DormSysID = RS_DormWaterElec.DormSysID And
RS_DormMonthFee.FeeMonth *= convert(varchar(7),RS_DormWaterElec.ReadMonth,121) And
RS_DormMonthFee.DormSysID *= RS_DormWaterElec.DormSysID And
RS_DormMonthFee.EmpSysID = RS_Emp.EmpSysID
ORDER BY
RS_Dorm.DormNo ASC

--你是这样写的？