Question

我的项目表是。

create table book_rec(book_name char(30),author char(30),total_copies number(15),available_copies number(5),primary key(book_name));
create table membership_rec(mem_id number(20),mem_name char(30),no_of_books_taken number(4),primary key(mem_id));
create table book_details(book_id number(30),book_name char(30),mem_id number(5),primary key(book_id),foreign key(book_name)references book_rec(book_name));
create table circulation_rec(book_id number(20),mem_id number(20),issue_date date,return_date date,foreign key (book_id)references book_details(book_id),foreign key(mem_id)references membership_rec(mem_id));

我想创建一个触发器，根据circulation_date记录自动增加和减少来自book_rec的no_of_books_taken和return_date.But程序显示错误。如何解决错误。你可以帮助任何人吗？< / p>

这是我的触发器代码。

create or replace trigger t_trigger
After insert or update on  circulation_rec
for each row
begin

if inserting then
update book_rec
set available_copies = available_copies - 1 
where book_name = :NEW.book_name;
update membership_rec
set no_of_books_taken = no_of_books_taken +1
where mem_id = :NEW.mem_id;
elsif updating then
update book_rec
set available_copies = available_copies - 1 
where book_name = :old.book_name;
update membership_rec
set no_of_books_taken = no_of_books_taken - 1
where mem_id = :New.mem_id;
end if;
end;
/

Answer 1

如果您执行SHOW ERRORS或运行此查询，

SELECT NAME, TYPE, line, text FROM user_errors;

您将了解完整的错误消息

NAME,       TYPE    LINE           TEXT
----        ---     ---            ----
T_TRIGGER   TRIGGER 6   PLS-00049: bad bind variable 'NEW.BOOK_NAME'
T_TRIGGER   TRIGGER 13  PLS-00049: bad bind variable 'OLD.BOOK_NAME'

现在，导致此错误是因为触发器的所有者 - circulation_rec表没有book_name列。因此，Oracle无法理解:NEW.book_name和:OLD.book_name的内容意味着在这种情况下，因此它会抛出错误的绑定变量错误。

现在，要解决此问题，您可以添加IN条件以从book_id表中获取book_details，因为circulation_rec确实有book_id。

像这样。

CREATE OR replace TRIGGER t_trigger 
  AFTER INSERT OR UPDATE ON circulation_rec 
  FOR EACH ROW 
BEGIN 
    IF inserting THEN 
      UPDATE book_rec 
      SET    available_copies = available_copies - 1 
      WHERE  book_name IN (SELECT book_name 
                           FROM   book_details 
                           WHERE  book_id = :NEW.book_id); 

      UPDATE membership_rec 
      SET    no_of_books_taken = no_of_books_taken + 1 
      WHERE  mem_id = :NEW.mem_id; 
    ELSIF updating THEN 
      UPDATE book_rec 
      SET    available_copies = available_copies - 1 
      WHERE  book_name IN (SELECT book_name 
                           FROM   book_details 
                           WHERE  book_id = :OLD.book_id); 

      UPDATE membership_rec 
      SET    no_of_books_taken = no_of_books_taken - 1 
      WHERE  mem_id = :New.mem_id; 
    END IF; 
END; 

/

这是一个dbfiddle demo

警告：编译但在pl / sql中创建触发器时出现编译错误？

1 个答案: