4 DDL&&DML

rename tablename to newname;/***修改表名***/
select ename,(sal+nvl(comm,0)) 年薪 from emp;/***nvl(),comm若为null,返回0***/
select ename || '的月薪是' ||(sal+nvl(comm,0)) 月薪 from emp;

savepoint aa;/***设置保存点***/
...
rollback to aa;/***回退到保存点***/