Creating random numbers

SQL Apprentice Question
wanted to create random numbers for some strange purpose using SQL
Server 2000. Even if the numbers are going to repeat its fine. [Pls note I
don't want to use newid() ].

For ex: I want to pass two integer values say, 10, 30 ... now i expect
randoms to be generated between these two numbers. How do to it in SQL
Server. Can any one help me in this?


Celko Answers
The first problem is that there are two kinds of random selection from
a set:

1) With replacement = you can get multiple copies of the same value.
This is shooting dice.

This one is easy if you have a random function in your SQL product.
Most of the pseudo-random generators return a floating point fraction
value between 0.00 and 0.9999.... at whatever precision your SQL engine
has. The choice of a seed to start the generator can be the system
clock or some other constantly changing value.

SELECT S1.key_col
FROM SomeTable AS S1, SomeTable AS S2
WHERE S1.key_col <= S2.key_col
GROUP BY S1.key_col
HAVING COUNT(S2.key_col)
= (SELECT COUNT(*)
FROM SomeTable AS S3) * RANDOM(seed) + 1.0;

Or you can add a column for this.

CREATE TABLE RandNbrs2
(seq_nbr INTEGER PRIMARY KEY,
randomizer FLOAT -- warning !! not standard SQL
DEFAULT (
(CASE (CAST(RAND() + 0.5 AS INTEGER) * -1)
WHEN 0.0 THEN 1.0 ELSE -1.0 END)
* (CAST(RAND() * 100000 AS INTEGER) % 10000)
* RAND())
NOT NULL);

INSERT INTO RandNbrs2 VALUES (1, DEFAULT);
INSERT INTO RandNbrs2 VALUES (2, DEFAULT);
INSERT INTO RandNbrs2 VALUES (3, DEFAULT);
INSERT INTO RandNbrs2 VALUES (4, DEFAULT);
INSERT INTO RandNbrs2 VALUES (5, DEFAULT);
INSERT INTO RandNbrs2 VALUES (6, DEFAULT);
INSERT INTO RandNbrs2 VALUES (7, DEFAULT);
INSERT INTO RandNbrs2 VALUES (8, DEFAULT);
INSERT INTO RandNbrs2 VALUES (9, DEFAULT);
INSERT INTO RandNbrs2 VALUES (10, DEFAULT);

SELECT * FROM RandNbrs2;

2) Without replacement = you can each value only once. This is dealing
playing cards.

This is trickier. I would start with a table that has the keys and a
sequentially numbered column in it:

CREATE TABLE CardDeck
(keycol NOT NULL PRIMARY KEY,
seq INTEGER NOT NULL);

INSERT INTO CardDeck (keycol, seq)
SELECT S1.keycol, COUNT(S2.keycol)
FROM SomeTable AS S1, Sometable AS S2
WHERE S1.key_col <= S2.key_col
GROUP BY S1.key_col;

Now shuffle the deck by determing a random swap pair for all the rows:

BEGIN
DECLARE i INTEGER, j INTEGER;
SET i = (SELECT COUNT(*) FROM CardDeck);
WHILE i < 0
LOOP
SET j = (SELECT COUNT(*) FROM CardDeck) * RANDOM(seed) + 1.0;
UPDATE CardDeck
SET seq = CASE WHEN seq = i THEN j
WHEN seq = j THEN i
ELSE seq END;
WHERE seq IN (i, j);
SET i = i - 1;
LOOP END;
END;

You don't really need j, but it makes the code easier to read.

Biography:

Marsaglia, G and Zaman, A. 1990. Toward a Univesal Random Number
Generator. Statistics & Probability Letters 8 (1990) 35-39.

Marsaglia, G, B. Narasimhan, and A. Zaman. 1990. A Random Number
Generator for PC's. Computer Physics Communications 60 (1990) 345-349.

Leva, Joseph L. 1992. A Fast Normal Random Number Generator. ACM
Transactions on Mathematical Software. Dec 01 1992 v 18 n 4. p 449

Leva, Joseph L. 1992. Algorithm 712: A Normal Random Number Generator.
ACM Transactions on Mathematical Software. Dec 01 1992 v 18 n 4. p 454

Bays, Carter and W.E. Sharp. 1992. Improved Random Numbers for Your
Personal
Computer or Workstation. Geobyte. Apr 01 1992 v7 n2. p 25

Hulquist, Paul F. 1991. A Good Random Number Generator for
Microcomputers.Simulation. Oct 01 1991 v57 n 4. p 258

Komo, John J. 1991. Decimal Pseudo-random Number Generator. Simulation.
Oct 01 1991 v57 n4. p 228

Chambers, W.G. and Z.D. Dai. 1991. Simple but Effective Modification to
a Multiplicative Congruential Random-number Generator. IEEE
Proceedings.Computers and Digital Technology. May 01 1991 v 138 n3. p
121

Maier, W.L. 1991.. A Fast Pseudo Random Number Generator. Dr. Dobb's
Journal.May 01 1991 v17 n 5. p 152

Sezgin, Fatin. 1990. On a Fast and Portable Uniform Quasi-random Number
Generator. Simulation Digest. Wint 1990 v 21 n 2. p 30

Macomber, James H. and Charles S. White. 1990. An n-Dimensional Uniform
Random Number Generator Suitible for IBM-Compatible Microcomputers.
Interfaces. May 01 1990 v 20 n 3. p 49

Carta, David G. 1990. Two Fast Implementations of the "Minimal
Standard" Random Number Generator. Communications of the ACM. Jan 01
1990 v 33 n 1. p 87

Elkins, T.A. 1989. A Highly Random-number Generator. Computer
Language. Dec 01 1989 v 6 n 12 p 59

Kao, Chiang. A Random Number Generator for Microcomputers. OR: The
Journal of the Operational Research Society. Jul 01 1989 v 40 n 7. p
687

Chassing, P. 1989. An Optimal Random Number Generator Zp. Statistics &
Probability Letters. Feb 01 1989 v 7 n 4. p 307

Also, you can contact Kenneth G. Hamilton 72727,177 who has done some
work with RNG's. He has implemented one (at least one) of the best.

"A Digital Dissolve for Bit-Mapped Graphics Screens" by Mike Morton in
Dr.Dobb's Journal, November 1986, page 48.

CMOS Cookbook by Don Lancaster; Sams 1977, page 318.

Art of Computer Programming, Volume 2: Seminumeral Algorithms, 2nd
edition by Donald Knuth; Addison-Wesley 1981; page 29.

Numerical Recipes in Pascal: The Art of Scientific Computing by Press
et al.; Cambridge 1989; page 233.