15 PL/SQL视图（虚拟表）

create or replace view my_view as select ename,job,sal,comm from emp;
create or replace view my_view as select ename,job,sal,comm from emp with read only;
create or replace view my_view as select emp.ename,dept.deptno,dept.dname from emp,dept where emp.deptno=dept.deptno with read only;

drop view my_view;