如何编写在更新date_returned列时执行的触发器？

Question

当date_returned列更新时，将执行此触发器。触发器应该计算罚款并更新借款人在借款人表中的未付罚款。每天晚上罚款5美元。

我的桌子：

DROP TABLE Loan_Transaction;
DROP TABLE Borrower;

CREATE TABLE Borrower ( 
Borr_ID          NUMBER (4) PRIMARY KEY, 
borr_name        VARCHAR2 (25) not null, 
borr_address     VARCHAR2 (50) not null, 
borr_city        VARCHAR2 (15) not null, 
phone            VARCHAR2 (8), 
borr_type        VARCHAR2 (2), 
books_on_loan    NUMBER(1), 
outstanding_fines     NUMBER (6,2), 
check (borr_type in('R','NR','S')), 
check (books_on_loan <10)
); 

CREATE TABLE Loan_Transaction ( 
loan_ID                 NUMBER (9) PRIMARY KEY, 
Borr_ID                 NUMBER (7) REFERENCES Borrower, 
Item_Copy_ID            NUMBER (7), 
loan_type               VARCHAR2 (1), 
loan_date               DATE, 
due_date                DATE, 
date_returned           DATE, 
check (loan_type in('O','R'))
);   

到目前为止我所拥有的......

CREATE OR REPLACE TRIGGER fines
BEFORE UPDATE ON Loan_Transaction
FOR EACH ROW
DECLARE fine_amt NUMBER;
BEGIN
SET fine_amt = (loan_date - date_returned) * 5
UPDATE Borrower b
SET outstanding_fines = (outstanding_fines + fine_amt);
END;
/      

这是错误：ORA-24344：编译错误成功

Answer 1

您的代码有语法错误。运行脚本创建触发器后，需要运行sho错误列出错误。

此行无效SET fine_amt = (loan_date - date_returned) * 5

相反它应该是fine_amt := (:NEW.loan_date - :NEW.date_returned) * 5; 你的更新声明也没有任何意义。您需要让where子句仅更新与loan_transaction表中更新的贷款相关的行。这段代码不正确，似乎也有错误。

您需要学习语法并相应地实施。您还需要使用：OLD，：NEW来引用loan_transaction中触发的列。