光标在触发器中 [英] cursor in a trigger

问题描述

我有一个现有的表 postn_matrix ，其中包含员工列表和他们的计数。

I have an existing TABLE postn_matrix which contains a list of employees and a count of their resp. positions in the organisation.

每当添加或删除用户的位置时，相应的计数会反映在表触发此触发器（VIA UPDATE）

Whenever a position of a user is added or removed, the corresponding count is reflected in the table thro' this trigger (VIA UPDATE)

现在，如果有一个新用户，他将不会在 postn_matrix 中有一个条目，因此我必须插入一个新的记录（VIA INSERT）。这需要从BASE表。

Now, if there is a new user, he will not have an entry in postn_matrix, so I have to insert a new record for him/her (VIA INSERT). This needs to be brought in from the BASE TABLE.

更新似乎工作正常，但我不能带来一个新的用户进入表。

The update seems to be working fine but I am not able to bring in a new user into the table.

我一直在试图用游标处理这种情况。但它还没有任何帮助。
我希望有些专家可以给我看看.. :)。非常感谢任何其他建议，除非使用光标。

I've been trying to handle this case with a cursor. But it hasnt been of any help yet. I'm hoping some expert could show me the light.. :). any other suggestions besides using a cursor will be much appreciated

CREATE OR REPLACE TRIGGER TRIG1
BEFORE INSERT OR DELETE ON (BASETABLE)
FOR EACH ROW
DECLARE
  cursor c1 is
  select person_id 
  from postn_matrix;

  v_temp varchar2(15);
BEGIN
  IF INSERTING THEN
    open c1;    
    LOOP
      fetch c1 into v_temp;

      if v_temp!=:new.person_id THEN
        insert into POSTN_MATRIX (PERSON_ID)
        VALUES (:new.PERSON_ID);
      else
        UPDATE POSTN_MATRIX
        //this is working fine ;

      END IF;
    end loop;
    close c1;

END
/

推荐答案

由于循环（它缺少一个退出子句 - 希望你失去了将它转换为一个问题），你将尝试插入一个记录到 pstn_matrix 为每个记录游标返回，是否有任何匹配：new.person_id 如果有匹配，你也会做更新。这可能不是你想要的，你可能会得到约束违反其他事情。你也不是设置你的计数器字段 - 如果那不是nullable那将会错误。但你没有说出错误，如果有的话，你会得到。

Because of the loop (which is missing an exit clause - hopefully you've just lost that translating this into a question) you're going to attempt to insert a record into pstn_matrix for every record the cursor returns, whether there are any matching :new.person_id or not; and if there is match you'll also do the update. Which probably isn't what you want, and you might get a constraint violation among other things. You also aren't setting your counter field - if that is not nullable then that will error. But you haven't said what errors, if any, you are getting.

如果你必须这样做通过触发器，那么你可以检查是否有一行新人：

If you must do this through a trigger then you can either check if there is a row for the new person at all:

DECLARE
  v_temp postn_matrix.person_id%TYPE;
BEGIN
  IF INSERTING THEN
    select max(person_id) into v_temp
    from postn_matrix
    where person_id = :new.person_id;

    if v_temp is null then
      -- no record found, so insert one
      insert into postn_matrix (person_id, position_count)
      values (:new.person_id, 1);
    else
      -- record exists, so update
      update postn_matrix ...
    end if;
  ...

...或使用 合并 。

... or use merge.

但是我不喜欢这个模型，你正在设置潜在的数据差异和并发修改基表。尝试保持这样的计数不一定像看起来那么简单。

But I don't like this model, and you're setting up the potential for data discrepancies with concurrent modifications to the base table. Trying to maintain a count like this is not necessarily as simple as it seems.

我通常喜欢这样做一个视图，这将是最新的，不需要触发器复杂的事情：

I'd usually prefer to make this a view, which will always be up to date and doesn't need the trigger complicating things:

create view postn_matrix as
  select person_id, count(*)
  from basetable
  group by person_id;

当然，我可能会曲解或过度简化您的基本表， postn_matrix for。看起来有点琐碎，甚至作为一个视图。如果你有单独的 person 和 person_position 表，那么你可以添加一个外连接来查看没有位置：

Of course, I may be misinterpreting or oversimplifying what your base table(s) does and what you need postn_matrix for. It seems a little trivial to have even as a view. If you have separate person and person_position tables, say, then you can add in an outer join to see people with no positions:

create view postn_matrix as
  select p.person_id, count(pp.position_id)
  from person p
  left join person_position pp on pp.person_id = p.person_id
  group by p.person_id;

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