在删除触发器上选择 table 时改变触发器

Question

请帮忙解决以下问题。我有一个有两行的 table，在删除一行时我写了一个触发器，我想将记录写入另一行的暂存 table(staging_tbl)删除后。但它会抛出一个有效的变异触发器错误。但是有没有一种方法可以避免它并将记录写入暂存 table 只有 main table 中有 2 行并且其中一个被删除（而不是 [=15= 上的所有删除） ]).

create or replace TRIGGER a_del_trg
  after delete on item_master
  for each row

DECLARE

  l_item NUMBER :=0;
  l_item_parent number :=0;
BEGIN

  INSERT INTO tmp_chk (item,item_parent) VALUES (:OLD.item,:OLD.item_parent);

  SELECT a.item,a.item_parent INTO l_item , l_item_parent
  FROM item_master a , tmp_chk  b  WHERE  a.item_parent = b.item_parent
  and a.item != b.item;

      INSERT INTO staging_tbl
        (create_date, table_name, item_sku, if_name)
      values
        (SYSDATE, 'Item_master', l_item, 'W'); -- want to add the remaining item here
    END IF;

END a_del_trg;

Answer 1

PRAGMA AUTONOMOUS_TRANSACTION

我使用以下语句重现了您的错误：

create table item_master(item number, item_parent number);
insert into item_master values (1, 10);
insert into item_master values (2, 10);

create table tmp_chk(item number, item_parent number);

create table staging_tbl(create_date date, table_name varchar2(30), item_sku number, if_name varchar2(10));

我使用了你的触发器（在从你的触发器末尾删除 END IF 残留代码之后）。我收到错误 "ORA-04091: table name is mutating, trigger/function may not see it." message.

提到这个很好的解释Fix Oracle mutating trigger table errors，必须重申以下摘录：

At the end of the day, the mutating table error is usually the result of a poor application design and mutating triggers should be avoided whenever possible.

根据参考文献autonomous transactions中的第四个选项，我将你的触发器重写如下：

create or replace TRIGGER a_del_trg
  after delete on item_master
  for each row

DECLARE

  l_item NUMBER :=0;
  l_item_parent number :=0;
  pragma autonomous_transaction;
BEGIN

  INSERT INTO tmp_chk (item,item_parent) VALUES (:OLD.item,:OLD.item_parent);
  
  SELECT a.item,a.item_parent INTO l_item , l_item_parent
  FROM item_master a , tmp_chk  b  WHERE  a.item_parent = b.item_parent
  and a.item != b.item;

      INSERT INTO staging_tbl
        (create_date, table_name, item_sku, if_name)
      values
        (SYSDATE, 'Item_master', l_item, 'W'); -- want to add the remaining item here
commit;
END a_del_trg;
/

运行查询：

select * from item_master;
2   10

select * from tmp_chk ;
1   10

select * from staging_tbl;
27-NOV-15   Item_master 2   W

回滚

来自here：

"... in 999 times out of 1000, if you find yourself "forced" to use an autonomous transaction - it likely means you have a serious data integrity issue you haven't thought about.

Where do people try to use them?

in that trigger that calls a procedure that commits (not an error logging routine). Ouch, that has to hurt when you rollback.

in that trigger that is getting the mutating table constraint. Ouch, that hurts even more

Error logging - OK.

Almost everything else - not OK."

在删除触发器上选择 table 时改变触发器

Mutating trigger while selecting a table on delete trigger

sql

oracle

triggers

plsql

mutating-table