新旧触发代码 [英] new and old trigger code

问题描述

谁能解释一下是什么意思:

can someone please explain what is meant by:

:new 和 :old 触发代码.

推荐答案

:new 和 :old 是伪记录，可让您访问特定的列.如果我有一张桌子

:new and :old are pseudo-records that let you access the new and old values of particular columns. If I have a table

CREATE TABLE foo (
  foo_id NUMBER PRIMARY KEY,
  bar    VARCHAR2(10),
  baz    VARCHAR2(10)
);

然后我插入一行

INSERT INTO foo( foo_id, bar, baz ) 
  VALUES( 1, 'Bar 1', 'Baz 1' );

然后在插入触发器之前的行级

then in a row-level before insert trigger

:new.foo_id will be 1
:new.bar will be 'Bar 1'
:new.baz will be 'Baz 1'

同时

:old.foo_id will be NULL
:old.bar will be NULL
:old.baz will be NULL

如果您随后更新该行

UPDATE foo
   SET baz = 'Baz 2'
 WHERE foo_id = 1

然后在更新前的行级触发器中

then in a before update row-level trigger

:new.foo_id will be 1
:new.bar will be 'Bar 1'
:new.baz will be 'Baz 2'

同时

:old.foo_id will be 1
:old.bar will be 'Bar 1'
:old.baz will be 'Baz 1'

如果我然后删除该行

DELETE FROM foo
 WHERE foo_id = 1

然后在删除行级触发器之前，

then in a before delete row-level trigger,

:new.foo_id will be NULL
:new.bar will be NULL
:new.baz will be NULL

同时

:old.foo_id will be 1
:old.bar will be 'Bar 1'
:old.baz will be 'Baz 2'

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