如果在select中使用sum或max，则需要按其他列分组：

SELECT invoicenumber AS invoice
 , invoicedate AS date
 , SUM(orderqty*ordersell) AS 'Invoice Total' 
FROM invoice 
JOIN orderdetail ON invoice.invoiceid = orderdetail.invoiceid 
GROUP BY invoicenumber,invoicedate;

我不知道这是否与你所看到的很接近，但我认为这是可行的（如果我正确理解你想要达到的目标）。

SELECT inv.invoicenumber,
       inv.invoice, 
       inv.invoicedate AS 'Date',
       MAX((SELECT ord.orderqty+ord.ordersell FROM DUAL)) AS 'Invoice Total' 
  FROM invoice inv
  JOIN orderdetail ord
    ON inv.invoice.invoiceid = ord.orderdetail.invoiceid 
 GROUP BY inv.invoice, 
          inv.invoice, 
          inv.invoicedate;

你可以试试这个（加上前面的答案）：

SELECT invoicenumber AS invoice
 , invoicedate AS date
 , SUM(orderqty*ordersell) AS 'Invoice Total' 
FROM invoice 
JOIN orderdetail ON invoice.invoiceid = orderdetail.invoiceid 
GROUP BY invoicenumber,invoicedate ORDER BY `Invoice Total` DESC LIMIT 1;

可能效率不太高，但只返回最高的结果。