select ename from emp for update of ename
union all
select dname from dept for update of dname
SQL> /
union all
*
ERROR at line 2:
ORA-00933: SQL command not properly ended

SQL> ed
Wrote file afiedt.buf

  1  select * from (
  2  select ename from emp --for update of ename
  3  union all
  4  select dname from dept --for update of dname
  5* ) for update
SQL> /
select * from (
              *
ERROR at line 1:
ORA-02014: cannot select FOR UPDATE from view with DISTINCT, GROUP BY, etc.