错误：超出最大递归 SQL 级别数 (50)

Question

我想强制执行诚信，这样一个人一天不能多次借书。表和触发器编译没有错误，但是当您尝试插入时出现上述错误。我无法修复它。语法：

create or replace trigger chk_DateL
for insert or update on lending
COMPOUND TRIGGER
--declare
L_Date number(1);
avail varchar2(10);
subtype copy_booksRec is lending%ROWTYPE;
type copied_bks is table of copy_booksRec;
cbks copied_bks := copied_bks();

after each row is 
begin
  cbks.extend;
  cbks(cbks.last).cb_num := :new.cb_num;
  cbks(cbks.last).sb_num := :new.sb_num;
end after each row;

after statement is
begin
  for i in cbks.first .. cbks.last loop
    select loancode into avail from copy_books where num = cbks(i).cb_num;
    select count(date_L) into L_Date from lending where sb_num = cbks(i).sb_num and date_L = cbks(i).date_L;
      if (L_Date = 0) then
        insert into Lending values (cbks(i).cb_num, cbks(i).sb_num, cbks(i).date_L);
        update copy_books set loancode = 'Not' where num = cbks(i).cb_num;
--        cbks(i).date_L := cbks(i).date_L;
    else
      dbms_output.put_line('You can only make ONE LOAN in a day! You have already loaned a book on ' || L_Date);
      cbks.delete;
    end if;
  end loop;
  end after statement;
end chk_DateL;
/
show errors

Answer 1

你的循环

FORALL i IN cbks.first .. cbks.last
    insert into lending values cbks(i);

插入到借出表中，这会导致再次执行触发器。因此触发器会自行叠加，直到达到 50 级，然后 oracle 通过抛出错误来停止此操作。