Re: SQL to Generate Random Numbers?

From: Russ Seligman <rseligma_at_oracle.com>
Date: Sun, 13 Mar 1994 23:23:56 GMT
Message-ID: <RSELIGMA.94Mar13152357_at_seinfeld.oracle.com>

In article <CMHA06.Cnu_at_freenet.carleton.ca> ah513_at_FreeNet.Carleton.CA (Doug Harris) writes:

>>In a previous article, am907_at_FreeNet.Carleton.CA (David Laderoute) says:
>>
>>... Is there, for example, a "random" number generator available
>>in SQL, which will allow the extraction of random records from the
>>database? Any help would be much appreciated--thanks.
>
> Although not possible in straight SQL, it should be possible to
>write a random number function in PL/SQL. If anyone has written such
>a thing I would be VERY interested in getting it.

Here is a PL/SQL implementation of the linear congruential method of generating random numbers. It's in the form of a PL/SQL package, so it should be easy to hook up to existing applications.

• the package spec =========

package random is
/* Linear congruential random number generator */

/* Returns random integer between [0, r-1] */ function rndint(r in number) return number;

/* Returns random real between [0, 1] */ function rndflt return number;

end; /* package random */

• the package body =========

package body random is
/* Linear congruential random number generator */

m constant number:=100000000;  /* initial conditions */
m1 constant number:=10000;     /* (for best results) */
b constant number:=31415821;   /*                    */

a number;                      /* seed */

the_date date;                 /*                             */
days number;                   /* for generating initial seed */
secs number;                   /*                             */

/*-------------------------- mult ---------------------------*/

/* Private utility function */

function mult(p in number, q in number) return number is

   p1 number;
   p0 number;
   q1 number;
   q0 number;

begin

   p1:=trunc(p/m1);
   p0:=mod(p,m1);
   q1:=trunc(q/m1);
   q0:=mod(q,m1);

   return(mod((mod(p0*q1+p1*q0,m1)*m1+p0*q0),m)); end; /* mult */

/*-------------------------- rndint --------------------------*/

/* Returns random integer between [0, r-1] */

function rndint (r in number) return number is begin

   /* generate a random number and set it to be the new seed */    a:=mod(mult(a,b)+1,m);

   /* convert it to integer between [0, r-1] and return it */    return(trunc((trunc(a/m1)*r)/m1));
end; /* rndint */

/*-------------------------- rndflt --------------------------*/

/* Returns random real between [0, 1] */

function rndflt return number is
begin

   /* generate a random number and set it to be the new seed */    a:=mod(mult(a,b)+1,m);

   /* return it */
   return(a/m);
end; /* rndflt */

begin /* package body random */

   /* Generate initial seed "a" based on system date */    /* (Must be connected to database.) */    the_date:=sysdate;
   days:=to_number(to_char(the_date, 'J'));    secs:=to_number(to_char(the_date, 'SSSSS'));    a:=days*24*3600+secs;
end; /* package body random */

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Russ Seligman                 "If there's nothing wrong with me, maybe
Oracle Corporation             there's something wrong with the universe."
rseligma_at_oracle.com              --Beverly Crusher, ST:TNG

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Received on Mon Mar 14 1994 - 00:23:56 CET