How good is the rand function of MySQL? How can it be improved?

Thx.

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When you argue with a fool, chances are he's doing the same

On Apr 29, 9:03 am, "Cosmic programmer" <not-my-em... (AT) nowhere (DOT) com>
wrote:
From the manual:

<http://dev.mysql.com/doc/refman/5.0/en/mathematical-
functions.html#function_rand>

"RAND() is not meant to be a perfect random generator, but instead is
a fast way to generate ad hoc random numbers which is portable between
platforms for the same MySQL version."

So I suppose it's up to you to decide how "good" it is.

Cosmic programmer wrote:
It's as good as pretty much any pseudo-random number generator. Why do
you think it needs to be improved?

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On 29 Apr, 13:03, "Cosmic programmer" <not-my-em... (AT) nowhere (DOT) com>
wrote:
How do you define good?
Depending on your criteria it is:
Very Good
Good
Not Very Good

"Jerry Stuckle" <jstucklex (AT) attglobal (DOT) net> wrote

I remember an older version had issues with generating the same random
number sequences when called from identical code routines.

The solution was to add a random seed from the language your using to
shuffle the pack first, so to speak.

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Tony
http://www.mccreath.org.uk

In message <n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d (AT) comcast (DOT) com>, Jerry Stuckle
<jstucklex (AT) attglobal (DOT) net> writes
If it's only as good as any pseudo-random number generator, it
definitely needs to be improved.

Nick

--
Nick Wedd nick (AT) maproom (DOT) co.uk

Tigger wrote:
Any pseudo random number generator will generate the same sequence if
you start with the same seed. But if you don't give it a seed, it picks
one up from the system (clock? don't know what it uses for sure).

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Nick Wedd wrote:
And exactly how would you do that? Most pseudo-random number generators
are pretty good, IMHO. And there is no such thing as a true random
number generator.

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In message <69qdnTw3ffk8Z4TVnZ2dnUVZ_qfinZ2d (AT) comcast (DOT) com>, Jerry Stuckle
<jstucklex (AT) attglobal (DOT) net> writes
Knuth's "Numerical recipes in C" explains what can be wrong with
system-supplied rand() functions. He wrote it 20 years ago, and things
must have improved since then; but I still wouldn't trust a
system-supplied rand(). He gives code for improving a system rand(),
also for replacing it by one known to be good. His code is in C of
course, but is quite short and is easily translated into other
languages.

Nick
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Nick Wedd nick (AT) maproom (DOT) co.uk

Nick Wedd wrote:
So? You don't think the system programmers haven't improved in 20
years? Unless you have a specific problem with it, why reinvent the wheel?

In fact, I'll bet that in 20 years even Knuth's random number generator
has been improved upon.


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