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

Thx.

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

Cosmic programmer wrote:
> How good is the rand function of MySQL? How can it be improved?
>
> Thx.
>
> --
> When you argue with a fool, chances are he's doing the same
>
>
>

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

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

On 29 Apr, 13:03, "Cosmic programmer" <not-my-em...@nowhere.com>
wrote:
> How good is the rand function of MySQL? How can it be improved?
>
> Thx.
>
> --
> When you argue with a fool, chances are he's doing the same

How do you define good?
Depending on your criteria it is:
Very Good
Good
Not Very Good

On Apr 29, 9:03 am, "Cosmic programmer" <not-my-em...@nowhere.com>
wrote:
> How good is the rand function of MySQL? How can it be improved?
>
> Thx.
>
> --
> When you argue with a fool, chances are he's doing the same

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.

"Jerry Stuckle" <jstucklex@attglobal.net> wrote in message
news:n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com. ..
> Cosmic programmer wrote:
>> How good is the rand function of MySQL? How can it be improved?
>>
>> Thx.
>>
>> --
>> When you argue with a fool, chances are he's doing the same
>
> It's as good as pretty much any pseudo-random number generator. Why do
> you think it needs to be improved?
>
> --
> ==================
> Remove the "x" from my email address
> Jerry Stuckle
> JDS Computer Training Corp.
> jstucklex@attglobal.net
> ==================
>

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.

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

In message <n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com>, Jerry Stuckle
<jstucklex@attglobal.net> writes
>Cosmic programmer wrote:
>> How good is the rand function of MySQL? How can it be improved?
>> Thx.
>> --
>> When you argue with a fool, chances are he's doing the same
>
>It's as good as pretty much any pseudo-random number generator. Why do
>you think it needs to be improved?

If it's only as good as any pseudo-random number generator, it
definitely needs to be improved.

Nick

--
Nick Wedd nick@maproom.co.uk

Tigger wrote:
> "Jerry Stuckle" <jstucklex@attglobal.net> wrote in message
> news:n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com. ..
>> Cosmic programmer wrote:
>>> How good is the rand function of MySQL? How can it be improved?
>>>
>>> Thx.
>>>
>>> --
>>> When you argue with a fool, chances are he's doing the same
>> It's as good as pretty much any pseudo-random number generator. Why do
>> you think it needs to be improved?
>>
>> --
>> ==================
>> Remove the "x" from my email address
>> Jerry Stuckle
>> JDS Computer Training Corp.
>> jstucklex@attglobal.net
>> ==================
>>
>
> 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.
>

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).

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

Nick Wedd wrote:
> In message <n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com>, Jerry Stuckle
> <jstucklex@attglobal.net> writes
>> Cosmic programmer wrote:
>>> How good is the rand function of MySQL? How can it be improved?
>>> Thx.
>>> --
>>> When you argue with a fool, chances are he's doing the same
>>
>> It's as good as pretty much any pseudo-random number generator. Why
>> do you think it needs to be improved?
>
> If it's only as good as any pseudo-random number generator, it
> definitely needs to be improved.
>
> Nick
>

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.

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================

In message <69qdnTw3ffk8Z4TVnZ2dnUVZ_qfinZ2d@comcast.com>, Jerry Stuckle
<jstucklex@attglobal.net> writes
>Nick Wedd wrote:
>> In message <n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com>, Jerry
>>Stuckle <jstucklex@attglobal.net> writes
>>> Cosmic programmer wrote:
>>>> How good is the rand function of MySQL? How can it be improved?
>>>> Thx.
>>>> --
>>>> When you argue with a fool, chances are he's doing the same
>>>
>>> It's as good as pretty much any pseudo-random number generator. Why
>>>do you think it needs to be improved?
>> If it's only as good as any pseudo-random number generator, it
>>definitely needs to be improved.
>> Nick
>>
>
>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.

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
--
Nick Wedd nick@maproom.co.uk

Nick Wedd wrote:
> In message <69qdnTw3ffk8Z4TVnZ2dnUVZ_qfinZ2d@comcast.com>, Jerry Stuckle
> <jstucklex@attglobal.net> writes
>> Nick Wedd wrote:
>>> In message <n8GdnZSDT8M7gIrVnZ2dnUVZ_vKdnZ2d@comcast.com>, Jerry
>>> Stuckle <jstucklex@attglobal.net> writes
>>>> Cosmic programmer wrote:
>>>>> How good is the rand function of MySQL? How can it be improved?
>>>>> Thx.
>>>>> --
>>>>> When you argue with a fool, chances are he's doing the same
>>>>
>>>> It's as good as pretty much any pseudo-random number generator. Why
>>>> do you think it needs to be improved?
>>> If it's only as good as any pseudo-random number generator, it
>>> definitely needs to be improved.
>>> Nick
>>>
>>
>> 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.
>
> 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

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.


--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================