更改交易金额记录后触发更新余额

Question

表格账户和交易

Account = {accNumber, balance, ...}
Transaction = {accNumber, amount, transNumber, ...}

在哪里Transaction.accNumber references Account.accNumber

我已经成功创建了INSERT之后更新余额的触发器

CREATE TRIGGER TR_Account_Balance
ON Transactions AFTER INSERT
AS
BEGIN
    UPDATE account SET
        balance = ins.newBalance
    FROM (
        SELECT a.accnumber,a.balance + SUM(i.amount) AS newBalance
        FROM Account a
        INNER JOIN inserted i ON i.accNumber = a.accNumber
        GROUP BY a.accNumber, a.balance
    ) AS ins
    WHERE account.accnumber = ins.accnumber
END

现在我需要创建一个触发器，它会根据交易 AFTER UPDATE 相应地更改余额。

例子：

   |accNumber | balance | ...
   |-----------------------------
   |        1 |   100   | ...

   |accNumber | amount | ...
   |-----------------------------
   |        1 |   20   | ...

如果我们将amount 更新为 10，balance 应该更改为 90。 我怎么可能这样做？

Answer 1

您应该以规范化的方式真正做到这一点，通过使用视图。为了获得更好的性能，您可以对其进行索引。

索引视图受到一些限制，特别是：

• 没有外部联接或应用
• 必须是模式绑定的
• 分组视图需要COUNT_BIG，并且只能使用SUM作为另一个聚合

CREATE VIEW dbo.vAccountBalance
WITH SCHEMABINDING AS

SELECT
  tr.accnumber,
  SUM(tr.amount) AS balance,
  COUNT_BIG(*) AS numTransactions -- this MUST be added
FROM dbo.Transactions tr;  -- schema-qualify

GO

CREATE UNIQUE CLUSTERED INDEX CX_vAccountBalance ON dbo.vAccountBalance (accnumber);

在任何插入、更新或删除期间，服务器将与其他索引一起维护此索引。

---

如果您真的想在触发器中执行此操作，您可以使用以下

• 注意Account 表是如何只被引用一次，并添加差异，而不是再次自连接
• 注意inserted 和deleted 是如何通过主键连接在一起的，并求和

CREATE TRIGGER TR_Account_Balance
ON Transactions AFTER INSERT, UPDATE, DELETE
AS

SET NOCOUNT ON;

IF NOT EXISTS (SELECT 1 FROM inserted) AND NOT EXISTS (SELECT 1 FROM deleted)
    RETURN;  -- early bail-out

UPDATE a  -- update the already referenced Account table
SET
    balance += ins.diffBalance
FROM Account a
INNER JOIN (
    SELECT
      i.accnumber,
      SUM(i.amount) AS diffBalance
    FROM (
        SELECT i.transNumber, i.accnumber, i.amount
        FROM inserted i
    )
    FULL JOIN (
        SELECT d.transNumber, d.accnumber, -(d.amount)
        FROM deleted d
    ) ON i.transNumber = a.transNumber
    GROUP BY i.accNumber
) AS ins ON a.accnumber = ins.accnumber;

GO

您也可以将其拆分为单独的 INSERT UPDATE 和 DELETE 触发器，在这种情况下，您可以删除前者的 deleted 部分，删除后者的 inserted 部分，然后更改UPDATE 使用 INNER JOIN 而不是 FULL JOIN。

Answer 2

如果您通过 proc 执行插入更新删除，这将是更新映射表或其他表的最佳位置。 如果您仍想在触发器中执行此操作（请仔细），请在同一表级别计算您的 SUM 并更新主表上的余额，以便它也涵盖更新和删除。

架构：

DROP TABLE IF EXISTS dbo.AccountTransaction
DROP TABLE IF EXISTS dbo.Account

CREATE TABLE dbo.Account
(
    AccountNumber INT            CONSTRAINT PK_AccountId PRIMARY KEY CLUSTERED IDENTITY(1, 1) NOT NULL,
    Balance       DECIMAL(18, 9) CONSTRAINT DF_Account_Balance DEFAULT 0.0 NOT NULL
)
GO

INSERT INTO dbo.Account
(
    Balance
)
VALUES
(
    DEFAULT -- decimal(18, 9)
)

CREATE TABLE dbo.AccountTransaction
(
    AccountTransactionId INT            CONSTRAINT PK_AccountTransactionId PRIMARY KEY CLUSTERED IDENTITY(1, 1) NOT NULL,
    AccountNumber        INT            CONSTRAINT FK_AccountTransaction_Account FOREIGN KEY REFERENCES dbo.Account (AccountNumber) NOT NULL,
    Amount               DECIMAL(18, 9) CONSTRAINT DF_AccountTransaction_Amount DEFAULT 0.0 NOT NULL
)
GO

CREATE TRIGGER dbo.tr_AccountTransaction
ON dbo.AccountTransaction
FOR INSERT, UPDATE, DELETE
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @Inserted AS INT =
            (
                SELECT COUNT (1)
                FROM   INSERTED
            )
    DECLARE @Deleted AS INT =
            (
                SELECT COUNT (1)
                FROM   DELETED
            )

    IF @Inserted > 0
    BEGIN
        UPDATE dbo.Account
        SET    Balance = x.NewBalance
        FROM
               (
                   SELECT   SUM (at.Amount) AS NewBalance
                   FROM     Inserted AS i
                   JOIN     dbo.AccountTransaction AS at
                       ON   at.AccountNumber = i.AccountNumber
                   GROUP BY i.AccountNumber
               ) AS x
    END

    IF @Inserted = 0
       AND @Deleted > 0
    BEGIN
        UPDATE dbo.Account
        SET    Balance = x.NewBalance
        FROM
               (
                   SELECT   SUM (at.Amount) AS NewBalance
                   FROM     Deleted AS d
                   JOIN     dbo.AccountTransaction AS at
                       ON   at.AccountNumber = d.AccountNumber
                   GROUP BY d.AccountNumber
               ) AS x
    END
END
GO

** 调试**

INSERT INTO dbo.AccountTransaction
(
    AccountNumber,
    Amount
)
SELECT a.AccountNumber,
       12.0
FROM   dbo.Account AS a

SELECT a.AccountNumber,
       a.Balance
FROM   dbo.Account AS a

UPDATE at
SET    at.Amount += 30
FROM   dbo.AccountTransaction AS at
WHERE  at.AccountTransactionId = 1

SELECT a.AccountNumber,
       a.Balance
FROM   dbo.Account AS a
 
SELECT at.AccountTransactionId,
       at.AccountNumber,
       at.Amount
FROM   dbo.AccountTransaction AS at

UPDATE at
SET    at.Amount -= 20
FROM   dbo.AccountTransaction AS at
WHERE  at.AccountTransactionId = 1

SELECT a.AccountNumber,
       a.Balance
FROM   dbo.Account AS a
 
SELECT at.AccountTransactionId,
       at.AccountNumber,
       at.Amount
FROM   dbo.AccountTransaction AS at
DELETE a
FROM   dbo.AccountTransaction AS a
WHERE  a.AccountTransactionId = 2

SELECT a.AccountNumber,
       a.Balance
FROM   dbo.Account AS a

SELECT at.AccountTransactionId,
       at.AccountNumber,
       at.Amount
FROM   dbo.AccountTransaction AS at