一些小常识，先累积点

---设置日期语言
SQL> select sysdate from dual;

SYSDATE
--------------
23-8月 -10

SQL> alter session set nls_date_language='AMERICAN';

会话已更改。

SQL> select sysdate from dual;

SYSDATE
------------
23-AUG-10

---Oracle随机数的方法DBMS_RANDOM.VALUE

dbms_random.value(100,200)可以产生100到200范围的随机数

---SYS_GUID (),是Oracle 8i 后提供的函数。SYS_GUID产生并返回一个全球唯一的标识符(原始值)由16个字节组成

----随机抽取N条记录
select * from (select * from test01 order by dbms_random.value) where rownum<6
select * from (select * from test01 order by sys_guid()) where rownum<6

---抽取从N行到M行的记录，如3到5行的记录
select * from (select rownum rid, t.* from test01 t) where rid between 3 and 5

---抽取重复记录

select count(*),t.id from test01 t
group by t.id
having count(*)>1

--------SCOTT用户下，左外连接，右外连接，全外连接
select a.deptno,b.dname
       from emp a, dept b
       where a.deptno=b.deptno(+)

select a.deptno,b.dname
       from emp a left outer join dept b
            on a.deptno=b.deptno

select a.deptno,b.dname
       from emp a, dept b
       where a.deptno(+)=b.deptno

select a.deptno,b.dname
       from emp a right outer join dept b
            on a.deptno=b.deptno
           

select a.deptno,b.dname
       from emp a full outer join dept b
            on a.deptno=b.deptno
--或者          
select a.ename,a.deptno,b.dname
       from emp a full outer join dept b
            using (deptno)  

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