如何使用条件

Question

之前已经部分回答了这个问题，但我想补充一个问题。我从这里得到的代码正在运行，但我想得到唯一有iif的记录（TblLoan.FutureValue为null，0，TblLoan.FutureValue） -     iif（Payment.TotalPaid为null，0，Payment.TotalPaid）= 0或更少。换句话说，只有0或更少余额的记录。

    SELECT TblLoan.LoanID, TblCustomer.LastName, Payment.TotalPaid AS Payments, iif(TblLoan.FutureValue is null, 0, TblLoan.FutureValue) - 
    iif(Payment.TotalPaid is null, 0, Payment.TotalPaid) AS Balance
FROM (TblLoan LEFT JOIN (SELECT LoanID,  sum(TotalAmount) as TotalPaid 
        FROM TblPayment group by LoanID
        )  AS Payment ON Payment.LoanID = TblLoan.LoanID) LEFT JOIN TblCustomer ON TblLoan.CustomerID = TblCustomer.CustID;

我知道应该有一个where子句但是我无法弄清楚放置WHERE Balance =＆lt;语句末尾的0似乎不起作用。

谢谢。

Answer 1

您应该在where子句中重复使用表达式本身，而不是别名“Balance”。请注意，您可以在此使用Nzfunction代替iif：

SELECT      TblLoan.LoanID,
            TblCustomer.LastName,
            Payment.TotalPaid AS Payments, 
            Nz(TblLoan.FutureValue) - Nz(Payment.TotalPaid) AS Balance
FROM        TblLoan 
LEFT JOIN   (
                SELECT  LoanID,
                        sum(TotalAmount) as TotalPaid 
                FROM    TblPayment group by LoanID
            )  AS Payment 
        ON  Payment.LoanID = TblLoan.LoanID 
LEFT JOIN   TblCustomer ON TblLoan.CustomerID = TblCustomer.CustID
WHERE       Nz(TblLoan.FutureValue) - Nz(Payment.TotalPaid) <= 0;