创建触发器以在从帐户到帐户的交易后更新余额 - SQL Oracle

Question

有人可以帮我吗？我正在尝试创建一个触发器，在 TRANSFERS 表中的事务之后更新 ACCOUNT 表中的余额。整个表模型更大，但这里有两个：

--ACCOUNT--
CREATE TABLE account(
account_num NUMBER(8) NOT NULL PRIMARY KEY,
ktnr REFERENCES account_type(ktnr),
regdate DATE NOT NULL,
balance NUMBER(10,2));

--TRANSFERS--
CREATE TABLE transfers(
row_nr NUMBER(9) NOT NULL PRIMARY KEY,
pers_nr REFERENCES customer(pers_nr),
from_account_num REFERENCES account(account_num),
to_account_num REFERENCES account(account_num),
amount NUMBER(10,2),
date DATE NOT NULL);

而且我认为代码是完全错误的，但这就是解决方案的想法。不知道如何写得更好。

create or replace trigger aifer_transfers
 after insert
 on transfers
 for each row
 when (new.amount is not null)
begin
  if :new.to_account_num != :new.pers_nr then
    update account a
    set a.balance = a.balance - :new.amount
    where :old.account_num = :new:account_num;

    elsif 
    :new.to_account_num = :new.pers_nr  then
    update account a
    set a.balance = a.balance + :new.amount
    where :old.account_num = :new:account_num;
    end if; 
 end; 

许多不同的错误，取决于选择的变量： 行/列：3/9 PL/SQL：忽略 SQL 语句 行/列：5/26 PLS-00049：错误的绑定变量“新”

Answer 1

您的表声明缺少某些数据类型（因为我们没有您的其他表），并且从 Oracle 12 开始，您可以使用 IDENTITY 列作为主键（并且有一些 CHECK 约束和 @987654329 DATE 列的 @ 值）：

CREATE TABLE account(
  account_num NUMBER(8,0)
              GENERATED ALWAYS AS IDENTITY
              NOT NULL
              CONSTRAINT account__account_num__pk PRIMARY KEY,
  ktnr        NUMBER(8,0)
              -- CONSTRAINT account__ktnr__fk REFERENCES account_type(ktnr)
              ,
  regdate     DATE
              DEFAULT SYSDATE
              NOT NULL,
  balance     NUMBER(10,2)
              NOT NULL
);

CREATE TABLE transfers(
  row_nr           NUMBER(9)
                   GENERATED ALWAYS AS IDENTITY
                   NOT NULL
                   CONSTRAINT transfers__row_nr__pk PRIMARY KEY,
  pers_nr          NUMBER(8,0)
                   NOT NULL
                   -- CONSTRAINT transfers__pers_nr__fk REFERENCES customer(pers_nr)
                   ,
  from_account_num NOT NULL
                   CONSTRAINT transfers_from__fk REFERENCES account(account_num),
  to_account_num   NOT NULL
                   CONSTRAINT transfers__to__fk REFERENCES account(account_num),
  amount           NUMBER(10,2)
                   NOT NULL
                   CONSTRAINT transfers__amount_chk CHECK ( amount > 0 ),
  datetime         DATE
                   DEFAULT SYSDATE
                   NOT NULL,
  CONSTRAINT transfers__from_ne_to__chk CHECK ( from_account_num != to_account_num )
);

然后就可以创建触发器了：

CREATE TRIGGER aifer_transfers
AFTER INSERT ON TRANSFERS
  FOR EACH ROW
BEGIN
  UPDATE account
  SET   balance = CASE account_num
                  WHEN :NEW.from_account_num
                  THEN balance - :NEW.amount
                  WHEN :NEW.to_account_num
                  THEN balance + :NEW.amount
                  ELSE balance
                  END
  WHERE account_num IN ( :new.from_account_num, :new.to_account_num );
END;
/

如果您创建 3 个帐户：

INSERT INTO account ( ktnr, balance ) VALUES ( 0, 100 );
INSERT INTO account ( ktnr, balance ) VALUES ( 0, 100 );
INSERT INTO account ( ktnr, balance ) VALUES ( 0, 100 );

然后：

INSERT INTO transfers (
  pers_nr, from_account_num, to_account_num, amount
) VALUES (
  0, 1, 2, 20
);

然后：

SELECT * FROM account;

输出：

ACCOUNT_NUM	KTNR	REGDATE	BALANCE
1	0	18-MAY-21	80
2	0	18-MAY-21	120
3	0	18-MAY-21	100

然后：

INSERT INTO transfers (
  pers_nr, from_account_num, to_account_num, amount
) VALUES (
  0, 1, 3, 15
);

应该是：

ACCOUNT_NUM	KTNR	REGDATE	BALANCE
1	0	18-MAY-21	65
2	0	18-MAY-21	120
3	0	18-MAY-21	115

然后：

INSERT INTO transfers ( pers_nr, from_account_num, to_account_num, amount )
SELECT 0, 3, 2, 10 FROM DUAL UNION ALL
SELECT 0, 2, 3, 20 FROM DUAL UNION ALL
SELECT 0, 1, 2, 10 FROM DUAL;

应该是：

ACCOUNT_NUM	KTNR	REGDATE	BALANCE
1	0	18-MAY-21	55
2	0	18-MAY-21	120
3	0	18-MAY-21	125

db小提琴here

---

更新

对于您的表，没有任何额外的CHECK 约束，您可能需要：

CREATE TRIGGER aifer_transfers
AFTER INSERT ON TRANSFERS
  FOR EACH ROW
BEGIN
  IF :NEW.amount <= 0 THEN
    RAISE_APPLICATION_ERROR( -20000, 'Amount must be above zero.' );
  END IF;
  IF :NEW.from_account_num IS NULL THEN
    RAISE_APPLICATION_ERROR( -20000, 'From account must be non-null.' );
  END IF;
  IF :NEW.to_account_num IS NULL THEN
    RAISE_APPLICATION_ERROR( -20000, 'To account must be non-null.' );
  END IF;
  IF :NEW.from_account_num = :NEW.to_account_num THEN
    RAISE_APPLICATION_ERROR( -20000, 'Accounts must be different.' );
  END IF;
  UPDATE account
  SET   balance = CASE account_num
                  WHEN :NEW.from_account_num
                  THEN balance - :NEW.amount
                  WHEN :NEW.to_account_num
                  THEN balance + :NEW.amount
                  ELSE balance
                  END
  WHERE account_num IN ( :new.from_account_num, :new.to_account_num );
END;
/

（但该验证应该全部作为CHECK 约束在transfers 表上而不是在触发器中实现。）

db小提琴here