sql - 如何在 MS Access 查询中指定默认值？

Question

我有三个类似于以下的表:

tbl发票:Number | Date | Customer
tblInv详细信息:Invoice | Quantity | Rate | Description
tbl付款:Invoice | Date | Amount

我创建了一个名为 exInvDetails 的查询添加 Amount列至tblInvDetails :

SELECT tblInvDetails.*, [tblInvDetails.Quantity]*[tblInvDetails.Rate]* AS Amount
FROM tblInvDetails;

然后我创建了一个查询 exInvoices添加Total和Balance列至tblInvoices :

SELECT tblInvoices.*,
  (SELECT Sum(exInvDetails.Amount) FROM exInvDetails WHERE exInvDetails.Invoice = tblInvoices.Number) AS Total, 
  (SELECT Sum(tblPayments.Amount) FROM tblPayments WHERE tblPayments.Invoice = tblInvoices.Number) AS Payments,
  (Total-Payments) AS Balance
FROM tblInvoices;

如果tblPayments中没有相应的付款，字段为 null 而不是 0 。有没有办法强制生成的查询放置 0在本专栏中？

Answer 1

使用nz()函数，如nz(colName, 0)。这将返回 colName，除非它为 null，在这种情况下，它将返回第二个参数(在本例中为 0)。