Question

I have a database with tables that are chained together with foreign keys, and the last one in the chain also has a foreign key to itself. I want to delete them with cascade on, exapt for the last one in the chain. That one should be set null, unless it’s parent record has a certain value. I figured i would do that with a trigger: whenever the last table updated, if the foreign key to itself had been set to null, check the field in the parent record, and if it is the value “default”, delete the record in the last table.

However, I haven’t found any help online indicting that comparing a parent record in another table.

Is this possible?

Answer 1

AFAIK you won’t be able to really delete the record in the last table (mutating table problem), but you could update a status field indicating the record has been logically deleted (untested):

create or replace trigger last_table_trig
before update on last_table
for each row
declare
  l_parentField varchar2(100);
begin
  if :new.self_ref_fk is null then
     select p.parent_field into l_parentField from parent_table p
     where p.pk = :new.parent_fk;
     if l_parentField = 'default' then
       :new.status := 'DELETED';
     end if;
  end if;
end;