oracle笔记 (导出、导入、创建用户、授权、insert,rownum)

1-- backup scott
    exp
2-- create user
    create user liuchao identified by liuchao default tablespace users quota 10M on users
    grant create session, create table , create view to liuchao
3-- import the data
    imp



insert into dept value values(50,'game','bj');
select * from dept;

//回滚
rollback;

//备份表（新建表并拷贝另一张表内容）
create table emp2 as select * from emp;
create table dept2 as select * from dept;
create table salgrade2 as select * from salgrade;

//查看数据库中表
select * from tab where tabtype='TABLE';

insert的三种方式
insert into dept2 valuse(50,'game','bj');
insert into dept2(deptno, dname) values(60,'game2');
insert into dept2 select * from dept;

rownum
select * from tab;
查询结果中有个伪字段 rownum
rownum 使用用一定的限制;
只能< 和<=配合使用;

select rownum r, ename from emp;

构造虚表能方便使用rownum;

select ename from (select rownum r, ename from emp) where r>10;

查询薪水最高的前五个员工;
  下面的sql有误:
  

select ename, sal from emp where rownum <=5 order by sal desc;

  错误的原因:他不是先排序再取前五行;
可以用子查询构造虚表;

 select ename, sal from
( select ename, sal from emp order by sal desc) where rownum<=5;

查询薪水最高的6~9名的雇员;

select ename, sal from
  ( 
    select ename,sal,rownum r from
      (
        select ename,sal from emp order by sal desc
      ) 
  )
where r>=6 and r<=9