Question

How do I write an Oracle trigger, than when a user deletes a certain record, the delete doesnt actually happen, but instead performs an update on those rows and sets the status of the record to ‘D’?

I tried:

create or replace
trigger DELFOUR.T4M_ITEM_ONDELETE
before delete on M_ITEM_H
FOR EACH ROW
BEGIN
  UPDATE
    M_ITEM_H
  SET
    ITEM_STAT = 'D'
  WHERE
    CUST_CODE = 'TEST'
    AND ITEM_CODE = 'GDAY'
  ;

  raise_application_error(-20000,'Cannot delete item');
END;

But I am getting mutating table errors. Is this possible?

Answer 1

First of all the trigger you wrote would throw a mutating table error. Technically what you are asking is not possible i.e. delete wouldn’t delete but rather update, unless you raise an exception in the middle which could be an ugly way of doing it. I would think users using some sort of application front end which lets them delete data using a delete button, so you may use an update statement there instead of a delete statement.

Another option would be to create a log table, where you could insert the record before deleting it from the actual table and then join the log table with the actual table to retrieve deleted records. Something like-

 CRETAE TABLE M_ITEM_H_DEL_LOG as SELECT * FROM M_ITEM_H WHERE 1=2;

And then

create or replace
trigger DELFOUR.T4M_ITEM_ONDELETE
before delete on M_ITEM_H
FOR EACH ROW
BEGIN
  INSERT INTO
    M_ITEM_H_DEL_LOG
  VALUES (:old.col1, :old.col2,.....) --col1, col2...are columns in M_ITEM_H
  ;
END;