Firebird trigger before delete

Question

I have two tables AUTHOR and BOOK connected by AUTHORID.

I need to create a trigger that in case of deleting an author, it deletes the books by that author first and after that deletes the author. And if someone just tries to update the AUTHORID field in AUTHOR it updates the AUTHORID in BOOK automatically.
Is that even doable? :)

set term # ;  
create trigger del for author  
before delete or update as  
  declare variable aut int;  
  declare variable bok int;  
begin  
  if(deleting) then  
  begin  
    delete from book where authorid=:aut;  
    delete from author where authorid=:aut;  
  end  
  if (updating) then  
  begin  
    update book set authorid=new.authorid;  
  end end#  
set term ; # 

Answer 1

You don't need a trigger to do this. For deleting you can use a foreign key that is ON DELETE CASCADE. This will automatically cascade the delete to the dependent row if the foreign key target is deleted.

In general I'd advise against allowing people to change identifiers, but if you really need or want that you can use ON UPDATE CASCADE. This will automatically update the foreign key if the foreign key target changes.

So for example (copied/modified from the Interbase 6 Language Reference):

CREATE TABLE T1 (P1 INTEGER NOT NULL PRIMARY KEY);
CREATE TABLE T2 (F2 INTEGER REFERENCES T1(P1)
  ON UPDATE CASCADE
  ON DELETE CASCADE);