從 SQL 中的 SELECT 中減去值

我有以下兩個查詢：

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

但我需要結果shipManagementInvoiceNetValue - shipManagementCreditNoteNetValue。我使用的HXTT JDBC DBF 驅動程序支持的不僅僅是 SQL92。

我怎麼能意識到這一點？

嘗試這個..

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

引用自：https://dba.stackexchange.com/questions/58673