关于2个表连接查询的问题

SELECT [过渡表].发票号码, IIf(IsNull([商品名称]),"否","是") AS 是否来单, Last([过渡表].商品名称) AS 商品名称, Last([过渡表].数量) AS 数量, Last([过渡表].单价) AS 单价, Last([过渡表].金额) AS 金额
FROM [select  发票号码.发票号码,"" as 商品名称, "" as 数量, "" as 单价, "" as 金额 from  发票号码
UNION select 发票内容.发票号码, 发票内容.商品名称, 发票内容.数量, 发票内容.单价, 发票内容.金额 from  发票内容]. AS 过渡表
GROUP BY [过渡表].发票号码;