问错误:超过了递归SQL级别的最大数量(50)

EN

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;
/
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