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Oracle随机函数之dbms_random利用详解

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今生有你2017 显示全部楼层 发表于 2021-10-26 12:59:14 |阅读模式 打印 上一主题 下一主题
dbms_random是oracle提供的一个随机函数包,以下先容一些dbms_random的常用示例:
dbms_random.value用法:
生成一个大于即是0,小于即是1的38位小数
复制代码 代码如下:
-- FUNCTION value RETURN NUMBER;
select dbms_random.value from dual;
SQL> select dbms_random.value from dual;
VALUE
----------
0.61011338

复制代码 代码如下:
-- FUNCTION value RETURN NUMBER;
select dbms_random.value from dual;
SQL> select dbms_random.value from dual;
VALUE
----------
0.61011338

生成一个指定范围内的数</ p>
复制代码 代码如下:
select dbms_random.value(100,0)
from dual;
SQL> select dbms_random.value(100,0)
2 from dual;
DBMS_RANDOM.VALUE(100,0)
------------------------
20.7742244285517

复制代码 代码如下:
-- FUNCTION value (low IN NUMBER, high IN NUMBER) RETURN NUMBER;
select dbms_random.value(100,0)
from dual;
SQL> select dbms_random.value(100,0)
2 from dual;
DBMS_RANDOM.VALUE(100,0)
------------------------
20.7742244285517

dbms_random.normal用法
获取正态分布的随机数
复制代码 代码如下:
select dbms_random.normal from dual;
SQL> select dbms_random.normal from dual;
NORMAL
----------
-1.7330759

复制代码 代码如下:
select dbms_random.normal from dual;
SQL> select dbms_random.normal from dual;
NORMAL
----------
-1.7330759

dbms_random.string用法
获取指定字符串
复制代码 代码如下:
/* "opt" specifies that the returned string may contain:
'u','U' : upper case alpha characters only
'l','L' : lower case alpha characters only
'a','A' : alpha characters only (mixed case)
'x','X' : any alpha-numeric characters (upper)
'p','P' : any printable characters
*/
SQL>
select
dbms_random.string('u',10)
from dual
union all
select
dbms_random.string('U',10)
from dual
union all
select
dbms_random.string('l',10)
from dual
union all
select
dbms_random.string('L',10)
from dual
union all
select
dbms_random.string('a',10)
from dual
union all
select
dbms_random.string('A',10)
from dual
union all
select
dbms_random.string('x',10)
from dual
union all
select
dbms_random.string('X',10)
from dual
union all
select
dbms_random.string('P',10)
from dual
union all
select
dbms_random.string('P',10)
from dual;

复制代码 代码如下:
--FUNCTION string (opt char, len NUMBER)
/* "opt" specifies that the returned string may contain:
'u','U' : upper case alpha characters only
'l','L' : lower case alpha characters only
'a','A' : alpha characters only (mixed case)
'x','X' : any alpha-numeric characters (upper)
'p','P' : any printable characters
*/
SQL>
select
dbms_random.string('u',10)
from dual
union all
select
dbms_random.string('U',10)
from dual
union all
select
dbms_random.string('l',10)
from dual
union all
select
dbms_random.string('L',10)
from dual
union all
select
dbms_random.string('a',10)
from dual
union all
select
dbms_random.string('A',10)
from dual
union all
select
dbms_random.string('x',10)
from dual
union all
select
dbms_random.string('X',10)
from dual
union all
select
dbms_random.string('P',10)
from dual
union all
select
dbms_random.string('P',10)
from dual;

DBMS_RANDOM.STRING(‘U',10)
—————————-
TXREHAICRI
VDTMXZORVB
udavjpudfb
hvfqhjjdgz
tZoanQzxtX
siATLEZXQa
2LWWZ3H3L5
ZF6MKKG1R7
#\j5IPva(W
sJe/srX:ZB
10 rows selected
dbms_random.seed用法
–可以设置seed来确定随机数的起始点,对于相同的seed而言,随机数的任意一次厘革都将是确定的。
– 就是说,如果在某一时刻调用了seed,之后第一次产生的随机数是4,第二次是6,第三次是1,
– 那么当你再次调用相同的seed之后,一次产生的随机数照旧4、6、1
– seed有两种,一种是数值型的,一种是字符型(最大长度2000)的
复制代码 代码如下:
SELECT USERENV('SESSIONID')
FROM DUAL;
BEGIN
dbms_random.seed(6);
END;
/
SELECT DBMS_RANDOM.value
FROM DUAL
CONNECT BY LEVEL < 10;

复制代码 代码如下:
SELECT USERENV('SESSIONID')
FROM DUAL;
BEGIN
dbms_random.seed(6);
END;
/
SELECT DBMS_RANDOM.value
FROM DUAL
CONNECT BY LEVEL < 10;

--SESSION 1
复制代码 代码如下:
SQL> SELECT USERENV('SESSIONID')
2 FROM DUAL;
USERENV('SESSIONID')
--------------------
15140521
SQL> BEGIN
2 dbms_random.seed(100);
3 END;
4 /
PL/SQL procedure successfully completed
SQL> SELECT DBMS_RANDOM.value
2 FROM DUAL
3 CONNECT BY LEVEL < 10;
VALUE
----------
0.53801770
0.67499536
0.65362270
0.76351985
0.29859834
0.40522032
0.99551636
0.39565580
0.18074760
9 rows selected

复制代码 代码如下:
SQL> SELECT USERENV('SESSIONID')
2 FROM DUAL;
USERENV('SESSIONID')
--------------------
15140521
SQL> BEGIN
2 dbms_random.seed(100);
3 END;
4 /
PL/SQL procedure successfully completed
SQL> SELECT DBMS_RANDOM.value
2 FROM DUAL
3 CONNECT BY LEVEL < 10;
VALUE
----------
0.53801770
0.67499536
0.65362270
0.76351985
0.29859834
0.40522032
0.99551636
0.39565580
0.18074760
9 rows selected

--SESSION 2
复制代码 代码如下:
SQL> SELECT USERENV('SESSIONID')
2 FROM DUAL;
USERENV('SESSIONID')
--------------------
15140517
SQL> BEGIN
2 dbms_random.seed(100);
3 END;
4 /
PL/SQL procedure successfully completed
SQL> SELECT DBMS_RANDOM.value
2 FROM DUAL
3 CONNECT BY LEVEL < 10;
VALUE
----------
0.53801770
0.67499536
0.65362270
0.76351985
0.29859834
0.40522032
0.99551636
0.39565580
0.18074760
9 rows selected

复制代码 代码如下:
SQL> SELECT USERENV('SESSIONID')
2 FROM DUAL;
USERENV('SESSIONID')
--------------------
15140517
SQL> BEGIN
2 dbms_random.seed(100);
3 END;
4 /
PL/SQL procedure successfully completed
SQL> SELECT DBMS_RANDOM.value
2 FROM DUAL
3 CONNECT BY LEVEL < 10;
VALUE
----------
0.53801770
0.67499536
0.65362270
0.76351985
0.29859834
0.40522032
0.99551636
0.39565580
0.18074760
9 rows selected

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