create table t (
  c1 int primary key
);

create materialized view log on t 
  with rowid including new values;

create materialized view mv 
refresh fast on demand 
as 
  select count(*) from t;
  
create or replace trigger t_aiuder
after insert or update or delete on t
declare
  pragma autonomous_transaction;
begin
  if inserting then
    dbms_mview.refresh ( 'mv', 'F' );
  else
    dbms_mview.refresh ( 'mv', 'C' );
  end if;
  commit;
end;
/

insert into t values ( 1 );

select count(*) from t;

COUNT(*)   
         1 

select * from mv;

COUNT(*)   
         0 

commit;

delete t;

select count(*) from t;

COUNT(*)   
         0 

select * from mv;

COUNT(*)   
         1 

commit;