问题[foxpro](dba)

我有一些用 VFP 制作的 .dbf 文件。我必须和他们一起工作并偶尔编辑它。最近我注意到其中一个 .dbf`s 以错误的方式运行。表中显示的记录数与实际记录数不符。我试图修改此表的标题以反映估计的记录数，但没有结果。我怎样才能取回我的原始文件？

我有一种方法可以重写 SQL 查询，所以我可以避免IFNULLor COALESCE，因为 HXTT DBF JDBC 驱动程序（支持 SQL92）会抛出以下错误：

Caused by: java.sql.SQLException: The aggregate function SUM(NETTO) can only be used in select-list, HAVING clause, and ORDER BY clause of SELECT statement.

以下查询导致上述错误：

SELECT
(   SELECT IFNULL (SUM (shipManagementInvoice.netto ), 0) AS shipManagementInvoiceNetValue
    FROM tckopf AS shipManagementInvoice
    WHERE shipManagementInvoice.referenzid = 1
        AND shipManagementInvoice.btyp = 5 )
-
(   SELECT IFNULL (SUM (shipManagementCreditNote.netto), 0) AS shipManagementCreditNoteNetValue
    FROM tckopf AS shipManagementCreditNote
    WHERE shipManagementCreditNote.referenzid = 1
        AND shipManagementCreditNote.btyp = 6 )
 AS shipManagementResult

如果我删除IFNULLor COALESCE，则没有错误。

我有以下两个查询：

1. shipManagementInvoiceNetValue：

   SELECT IFNULL (SUM (shipManagementInvoice.netto ), 0) AS shipManagementInvoiceNetValue
   FROM tckopf AS shipManagementInvoice
   WHERE shipManagementInvoice.referenzid = 1
       AND shipManagementInvoice.btyp = 5
   

2. shipManagementCreditNoteNetValue：

   SELECT IFNULL (SUM (shipManagementCreditNote.netto), 0) AS shipManagementCreditNoteNetValue
   FROM tckopf AS shipManagementCreditNote
   WHERE shipManagementCreditNote.referenzid = 1
       AND shipManagementCreditNote.btyp = 6
   

但我需要结果shipManagementInvoiceNetValue - shipManagementCreditNoteNetValue。我使用的HXTT JDBC DBF 驱动程序支持的不仅仅是 SQL92。

我怎么能意识到这一点？