create trigger tr_mytbl on mytbl for insert, update, delete
as
if not exists (select * from deleted)    -- insert or no op
   insert indextbl select pk, col1, col2 from inserted
else if exists (select * from inserted)  -- update
   update indextbl
   set col1 = i.col1 ,
       col2 = i.col2
   from indextbl t
       join inserted i
          on i.pk = t.pk
else -- delete
   delete indextbl
   from indextbl t
       join deleted
          on d.pk = t.pk