SQL> select banner from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production

SQL> create table t (
  2    x int primary key, y int
  3  );

Table created.

SQL> insert into t values (1, 1);

1 row created.

SQL> insert into t values (2, 2);

1 row created.

SQL> create materialized view log on t including new values;

Materialized view log created.

SQL> create materialized view mv
  2  refresh fast with primary key for update
  3  as
  4    select * from t;

Materialized view created.

SQL> update mv
  2  set    y = 3;

2 rows updated.

SQL>
SQL> insert into mv values (3, 3);

1 row created.

SQL> update mv
  2  set    y = 3;

2 rows updated.

SQL> insert into mv values (3, 3);

1 row created.

SQL> select * from mv;

         X          Y
---------- ----------
         1          3
         2          3
         3          3

SQL> select * from t;

         X          Y
---------- ----------
         1          1
         2          2

SQL> exec dbms_mview.refresh('mv');

PL/SQL procedure successfully completed.

SQL> select * from mv;

         X          Y
---------- ----------
         1          1
         2          2

SQL>