如何避免使用觸發器刪除每個請求超過 1 行？

Question

我想編寫一個觸發器，拒絕每個請求刪除超過 1 行

是否可以編寫這樣的觸發器？ 如果是，你能幫忙提供一個想法或代碼嗎？

我正在使用 oracle 數據庫 11g 並在 sqldeveloper 中編寫

訂單表

id
detail
orderdate

Answer 1

我不確定您為什么要這樣做（多行刪除比單行刪除更有效），但您可以為此使用復合觸發器，例如：

create table mytable (id number);

create or replace trigger one_row_per_delete
  for delete on mytable
  compound trigger

  row_count integer;

  before statement is
  begin
    row_count := 0;
  end before statement;

  before each row is
  begin
    row_count := row_count + 1;
  end before each row;

  after statement is
  begin
    if row_count > 1 then
      raise_application_error(-20000, 'Cannot delete more than one row per statement');
    end if;
  end after statement;

end one_row_per_delete;

測試：

insert into mytable values (1);

1 row inserted.

insert into mytable values (2);

1 row inserted.

insert into mytable values (3);

1 row inserted.

delete mytable where id = 1;

1 row deleted.

delete mytable;

ORA-20000: Cannot delete more than one row per statement
ORA-06512: at "SCOTT.ONE_ROW_PER_DELETE", line 18
ORA-04088: error during execution of trigger 'SCOTT.ONE_ROW_PER_DELETE'

Answer 2

例如，您可以使用觸發器執行它

CREATE OR REPLACE TRIGGER denies_delete_trg
BEFORE DELETE
   ON table_name
DECLARE
   v_count_elements NUMBER := 0;

BEGIN
   SELECT COUNT(1) INTO v_count_elements
   FROM table_name
   WHERE contitions_of_delete;

   IF v_count_elements > 0 THEN
       RAISE_APPLICATION_ERROR (-20000,'Too rows to delete.'); 
   END IF;
END;