create table t(id) as select 1 from dual;
create materialized view log on t with rowid (id) including new values;
create materialized view mv
refresh fast on commit as
select id, count(*) cnt from t group by id;

insert into t values (10);
commit;
insert into t values (10);
commit;
delete from t where id = 1;
commit;

select tbl_name, refresh_id, num_rows_ins, num_rows_upd, num_rows_del, num_rows
  from dba_mvref_change_stats where mv_name = 'MV'
 order by refresh_id;

TBL_NAME   REFRESH_ID NUM_ROWS_INS NUM_ROWS_UPD NUM_ROWS_DEL   NUM_ROWS
---------- ---------- ------------ ------------ ------------ ----------
T                  30            0            0            0          2
T                  31            0            0            0          3
T                  32            0            0            0          2