Re: Selecting a random sample of data using PL/SQL
Date: 1996/05/29
Message-ID: <4oinas$nod_at_gossamer.itmel.bhp.com.au>#1/1
>John L Dunn wrote:
>>
>> Anybody written PL/SQL code to select records from a table randomly? For
>> instance, I've got a 2,000,000 row table and I want a random sample of
>> 10,000; how do I do it using PL/SQL? Or is it better to punt and use a
>> 3GL/4GL for this purpose?
A re-post:
From: rseligma_at_oracle.com (Russ Seligman)
Newsgroups: comp.databases.oracle
Subject: Re: PL/SQL Random Number Generator
Date: 01 Nov 1995 19:37:48 GMT
Organization: Oracle Corporation, Redwood Shores, CA
I saw that someone else had posted the PL/SQL code that they had typed in. Here's the code as I originally created it (and presumably as Oracle support is distributing it)...
--Russ
-----Begin 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 */
-----End Package Spec-----
-----Begin 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 an 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 */
-----End Package Body-----
Lee Levy, ISSD Technical Dream Team, Del Code (34) BHP Information Technology, ACN 006 476 213 PO Box 261, Warrawong, NSW 2502, Australia PH: +61 42 75-5485 Fax: -5500 Tie: 8855- Internet : levy.lee.ls_at_bhp.com.au
Opinions expressed are mostly my own, so give me some credit. Received on Wed May 29 1996 - 00:00:00 CEST