Question

Can a trigger be created on drop user event? if so, how do I write the the trigger –
* I want to delete some rows related to that user from a table after drop user *

“Drop User”

Can you provide an example:

If the user is drop and oracle purge the user’s schema objects is there anyway I can select what row of data I want to keep or delete?

So are you saying that a Trigger can not be created on drop user event?

Answer 1

Of course you can. Assuming you’re actually dropping a user and not a table:

You’re looking for a system trigger as opposed to a schema trigger or a database trigger. You can add these to a large number of ddl events including DROP.

To quote from the documentation:

Causes the database to fire the trigger whenever a DROP statement
removes a database object from the data dictionary.

Your trigger might look something like the following:

create or replace trigger tr_drop_user
  before drop on database

begin
   if dbms_standard.dictionary_obj_type = 'USER' then

      insert into logs ( user, object_name )
      values ( sys_context('USERENV','OS_USER') -- OS User doing the dropping
             , dbms_standard.dictionary_obj_name -- name of object being dropped
              );

   end if;
end;
/

This uses the not particularly well documented dbms_standard package to work out what’s happening. PSOUG has better documentation, in my opinion.

If you only want to do this for a specific schema rather than for the entire database use before drop on schema instead.

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Just as a little side note I’m not convinced of the need to do this in a trigger. It would be better if you created a package with drop_user and create_user procedures that do everything you want in one place rather than disguising the logic in a trigger.