根据卡号使用 MS Access / SQL 更新借记卡上的余额

Question

我正在尝试更新不同借记卡上的剩余金额。我有以下 2 个表格：卡片和交易。 我希望我的结果是：

 Number|Initial_Amount|Remaining_Amount         T_ID|T_Date|Credit_Card|Amount
----------------------------------------       ---------------------------------
    123|          1000|     820                    1| 05/02|        123| 100
    456|           200|     150                    2| 06/02|        456| 50
                                                   3| 06/02|        123| 80

我已经写了一个查询来根据信用卡计算金额：

SELECT DISTINCT Sum(T2.Amount) AS SumOfAmount
FROM Transactions AS T1 INNER JOIN Transactions AS T2 ON T1.Credit_Card = T2.Credit_Card
GROUP BY T1.ID, T1.Credit_Card, T1.Amount;

但我现在不知道该去哪里。

我该如何解决？

Answer 1

您似乎想要这样的东西——假设您有一个包含原始金额的表：

select c.credit_card, c.original_amount,
       (c.original_amount - nz(sum(t.amount), 0)) as remaining
from cards as c left join
     transactions as t
     on t.credit_card = c.credit_card
group by c.credit_card, c.original_amount;

如果要更新cards，请使用相关子查询：

update cards
    set remaining_amount = (c.original_amount -
                            (select nz(sum(t.amount), 0)
                             from transactions as t
                             where t.cred_card = cards.credit_card
                            )
                           );