oracle database link、数据库的数据恢复及导入/导出

1、database link
create public database link remote_02 connect to scott identified by "tiger" using 'localhost:1521/orcl';
create or replace public synonym syn_emp1 for emp@remote_02;
select * from syn_emp1;

2、数据的恢复
复制一个表用于测试：create table emp1 as select * from emp;
进行删除操作：delete from emp1 where empno=8899;
利用闪回事务查询方法恢复上面删除的数据
select * from flashback_transaction_query where operation = 'DELETE' and logon_user='SCOTT';
找到删除相对应的插入语句：
insert into "SCOTT"."EMP1"("EMPNO","ENAME","JOB","MGR","HIREDATE","SAL","COMM","DEPTNO","TEST","TEST1") values ('8899','frank','engering',NULL,NULL,'1000',NULL,NULL,'1',NULL);
执行完毕即可恢复

当使用drop语句删除数据库数据时，我们可以在pl/sql中browse中的Recycle bin文件夹中找到被drop的文件，右击restore；

3、数据的导入/导出即imp/exp的简单用法介绍
imp username/pwd@IP:port/sid file=要导入dmp的路径 full=y 
如：imp scott/tiger@localhost:1521/orcl file=c:\1.dmp full=y
exp username/pwd@IP:port/sid file=要导出dmp的路径        
如：exp scott/tiger@localhost:1521/orcl file=c:\2.dmp
以上命令在dos下运行，今天头脑发热在pl/sql的sql window下和sql*plus下运行老提示我无效的sql语句，郁闷了半天，后面才想起来imp/exp命令都在环境变量path里，这才想起在dos下运行。

oracle sql中没有while语句  
sql中的递归写法：
SELECT a.empno,a.ename FROM emp a
   START WITH a.mgr IS NULL
  CONNECT BY PRIOR a.empno=a.mgr;