深入理解Oracle中的随机函数

2.sys_guid函数: 返回32 位的16 进制表示，raw类型
SQL> select sys_guid() from dual;
 
SYS_GUID()
--------------------------------
D0C3CDC75677446FAF9EC1C5C26A0236

对于raw类型,可以使用utl_raw包处理。
SQL> select utl_raw.cast_to_number(sys_guid()) from dual;
 
UTL_RAW.CAST_TO_NUMBER(SYS_GUI
------------------------------
          1.79662473137317E22
         
3.sample和sample block
(1)sample 按行的百分比来读,对于大表比较快
  sample 就是读全部，不加一样sample(n),--n为[0.000001,100）当然读的也不是严格的百分比，有一定的误差。
(2)sample block:按表的块来读,按照块数目扫描
  sample block中的sample不可加值，block必须加值，和单独的sample不同
  sample block(n), --n为[0.000001,100）

测试:
create table test as select * from all_objects;

select * from ( select * from test sample(50)) where rownum != 10;
select * from ( select * from test sample block(50) ) where rownum != 10;

有两条数据，任意删除一条
drop table test;
create table test(a number,b number);
insert into test values(1,2);
insert into test values(2,1);
delete from test where (a,b)=(select a,b from (select a,b from test order by dbms_random.value) where rownum<2);