create or replace view myview as select * from tb_Employee where sal<1000 with read only constraint;
create view myview2 as select tb_Employee.empno,tb_Employee.ename,tb_Department.dname from tb_Employee,dept where tb_Employee.deptno=tb_Employee.pk_Department_ID;
drop view myview;
原文：http://www.cnblogs.com/tufujie/p/5074494.html