在提供的standard Package中，并没有产生随机数的function或procedure.下面的例子是使用PL/SQL些的一个随机数产生器。
CREATE OR REPLACE package pk_rand
is
/**************************************************************
* 这个package返回一个0-1之间的随机数，可以通过设置set_rang(low,upper)
*来重新指定返回那个范围的随机数。
*大家都知道，产生随机数需要‘种子’，可以通过set_seed这个procedure来设*置初始值***************************************************************/
procedure set_range(p_lower in number
,p_upper in number
,p_integer in varchar2 := 'Y');
procedure set_seed(p_seed in number);
procedure rand(p_result out number) ;
function f_rand
return number;
pragma restrict_references(f_rand,WNDS);
end;
/
CREATE OR REPLACE package body pk_rand
is
v_range_lower number := 0;
v_range_upper number := 1;
v_lastval number;
v_rand number;
v_result number;
v_integer boolean := FALSE;
cursor c_seed is
select to_char(sysdate,'SSSSSDDDHHSSSSS')
from dual;
procedure set_seed(p_seed in number)
is
begin
v_lastval := p_seed;
end;
procedure set_range(p_lower in number,p_upper in number
,p_integer in varchar2 := 'Y')
is
begin
v_range_lower := p_lower;
v_range_upper := p_upper;
if p_integer = 'Y' then
v_integer := TRUE;
else
v_integer := FALSE;
end if;
end;
procedure rand(p_result out number)
is
begin
p_result := f_rand;
end;
function f_rand
return number is
/* Fixed values used in generation */
a number := 25214903917;
c number := 11;
m number := power(2,48);
begin
/* Compute next random number */
v_rand := ((a * v_lastval + c ) mod m );
/* Store it as seed value in next calculation */
v_lastval := v_rand;
/* Get output between 0 and 1 */
v_rand := v_rand / m;
/* Multiply up to required range */
if v_integer then
/* Increment the range by 1 to allow for truncation */
v_result := v_rand * ((v_range_upper +1) - v_range_lower ) +
v_range_lower;
v_result := trunc(v_result);
else
/* Just multiply to expand the answer */
v_result := v_rand * (v_range_upper - v_range_lower ) + v_range_lower;
end if;
return v_result;
end;
/* And now the initialisation code */
begin
open c_seed;
fetch c_seed
into v_lastval;
close c_seed;
end;
/
【责编:admin】
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