Oracle SQL - 带 Join 的条件插入触发器

Question

我需要创建一个触发器，检查插入表时“健身”类别中书籍的作者数量是否>3，如果为真，则拒绝插入。

我需要连接两个表才能获得计数。

桌子： 书：

Create table Book
(Book_ISBN CHAR(10) PRIMARY KEY,
Book_Title VARCHAR2(30) NOT NULL,
Book_PubDate DATE NOT NULL,
Pub_ID NUMBER (2) NOT NULL REFERENCES Publisher(Pub_ID),
Book_Cost NUMBER (5,2) NOT NULL,
Book_Retail NUMBER (5,2) NOT NULL,
Book_Category VARCHAR2(12) NOT NULL);

INSERT INTO BOOK VALUES ('1059831198','BODYBUILD IN 10 MINUTES A DAY','21-JAN-01',4,18.75,30.95,'FITNESS');
INSERT INTO BOOK
VALUES ('0401140733','REVENGE OF MICKEY','14-DEC-01',1,14.20,22.00, 'FAMILY LIFE');
INSERT INTO BOOK
VALUES ('4981341710','BUILDING A CAR WITH TOOTHPICKS','18-MAR-02',2,37.80,59.95, 'CHILDREN');
INSERT INTO BOOK
VALUES ('8843172113','DATABASE IMPLEMENTATION','04-JUN-99',3,31.40,55.95, 'COMPUTER');
INSERT INTO BOOK
VALUES ('3437212490','COOKING WITH MUSHROOMS','28-FEB-00',4,12.50,19.95,'COOKING');
INSERT INTO BOOK
VALUES ('3957136468','HOLY GRAIL OF ORACLE','31-DEC-01',3,47.25,75.95,'COMPUTER');
INSERT INTO BOOK
VALUES ('1915762492','HANDCRANKED COMPUTERS','21-JAN-01',3,21.80,25.00,'COMPUTER');
INSERT INTO BOOK
VALUES ('9959789321','E-BUSINESS THE EASY WAY','01-MAR-02',2,37.90,54.50,'COMPUTER');
INSERT INTO BOOK
VALUES ('2491748320','PAINLESS CHILD-REARING','17-JUL-00',5,48.00,89.95,'FAMILY LIFE');
INSERT INTO BOOK
VALUES ('0299282519','THE WOK WAY TO COOK','11-SEP-00',4,19.00,28.75,'COOKING');
INSERT INTO BOOK
VALUES ('8117949391','BIG BEAR AND LITTLE DOVE','08-NOV-01',5,5.32,8.95,'CHILDREN');
INSERT INTO BOOK
VALUES ('0132149871','HOW TO GET FASTER PIZZA','11-NOV-02',4,17.85,29.95, 'SELF HELP');
INSERT INTO BOOK
VALUES ('9247381001','HOW TO MANAGE THE MANAGER','09-MAY-99',1,15.40,31.95,'BUSINESS'); 
INSERT INTO BOOK
VALUES ('2147428890','SHORTEST POEMS','01-MAY-01',5,21.85,39.95, 'LITERATURE');

Commit;

表： 书作者：

CREATE TABLE BOOKAUTHOR
(Book_ISBN CHAR(10) REFERENCES Book(Book_ISBN),
Author_ID CHAR(4) REFERENCES Author(Author_ID),
CONSTRAINT bookauthor_pk PRIMARY KEY (Book_ISBN,Author_ID));

INSERT INTO BOOKAUTHOR
VALUES ('1059831198','S100');
INSERT INTO BOOKAUTHOR
VALUES ('1059831198','P100');
INSERT INTO BOOKAUTHOR
VALUES ('0401140733','J100');
INSERT INTO BOOKAUTHOR
VALUES ('4981341710','K100');
INSERT INTO BOOKAUTHOR
VALUES ('8843172113','P105');
INSERT INTO BOOKAUTHOR
VALUES ('8843172113','A100');
INSERT INTO BOOKAUTHOR
VALUES ('8843172113','A105');
INSERT INTO BOOKAUTHOR
VALUES ('3437212490','B100');
INSERT INTO BOOKAUTHOR
VALUES ('3957136468','A100');
INSERT INTO BOOKAUTHOR
VALUES ('1915762492','W100');
INSERT INTO BOOKAUTHOR
VALUES ('1915762492','W105');
INSERT INTO BOOKAUTHOR
VALUES ('9959789321','J100');
INSERT INTO BOOKAUTHOR
VALUES ('2491748320','R100');
INSERT INTO BOOKAUTHOR
VALUES ('2491748320','F100');
INSERT INTO BOOKAUTHOR
VALUES ('2491748320','B100');
INSERT INTO BOOKAUTHOR
VALUES ('0299282519','S100');
INSERT INTO BOOKAUTHOR
VALUES ('8117949391','R100');
INSERT INTO BOOKAUTHOR
VALUES ('0132149871','S100');
INSERT INTO BOOKAUTHOR
VALUES ('9247381001','W100');
INSERT INTO BOOKAUTHOR
VALUES ('2147428890','W105');

Commit;

我可以查询这两个表来获取我需要的内容：

SELECT
    BOOKAUTHOR.book_isbn,
    BOOK.book_category,
    COUNT(BOOKAUTHOR.book_isbn)
FROM BOOKAUTHOR
JOIN BOOK ON BOOK.book_isbn = BOOKAUTHOR.book_isbn
WHERE BOOK.book_category = 'FITNESS'
GROUP BY BOOKAUTHOR.book_isbn, BOOK.book_category
;

但是，我是触发器新手，不知道获得所需结果的正确语法。

到目前为止我的触发器看起来像：

CREATE TRIGGER fitness_author_control AFTER INSERT ON BOOKAUTHOR
FOR EACH ROW

DECLARE
    abundant_authors EXCEPTION;
    J Number(2);
    #temp;
        
BEGIN
    SELECT
        BOOKAUTHOR.book_isbn,
        BOOK.book_category,
        COUNT(BOOKAUTHOR.book_isbn) AS "J" 
        INTO temp
    FROM BOOKAUTHOR
    JOIN BOOK ON BOOK.book_isbn = BOOKAUTHOR.book_isbn
    WHERE BOOK.book_category = 'FITNESS'
    GROUP BY BOOKAUTHOR.book_isbn, BOOK.book_category;
        
    IF J > 3
    THEN DBMS_OUTPUT.PUT_LINE ('That is too many authors!');
    RAISE abundant_authors;
    END IF;
    
EXCEPTION
    WHEN abundant_authors
    THEN raise_application_error(-20002, 'I Cannot handle this many authors!');
END;
/

显然这不起作用，但是我缺乏解决它的知识，也不知道要问什么才能找到教程。这似乎是一个非常小众的问题。

我不知道的是如何声明该语句，以便当我运行以下命令时，触发器将停止插入：

INSERT INTO BOOKAUTHOR VALUES ('9000000099', 'P105');

任何指导将不胜感激！

我认为我需要在触发器内声明一个临时表来保存 select 语句的输出，尽管我怀疑这不是一个好方法？ 我不确定如何在这里使用 :new 前缀，但我也怀疑我需要这样做？

Answer 1

您没有针对您的情况提供错误消息，但我认为您的问题是突变。

当SQL Server尝试更改数据（插入/更新/删除）时，该表中的数据状态是未定义的，因此不能使用该表进行选择。

解决方案的可能变体之一 - 将触发器类型从“FOR EACH ROW”更改为语句级别，或遵循链接中的多项建议。