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    <p>I haven't been able to find the source code for the function quickly; seeing it might help get a better answer. That said, it looks like a 'no.. but kinda close'.</p> <p>From documentation I can see it tries to be random (and optionally you can seed it); but there are two caveats that mean it might not always be uniform when you expect it to the first issue is in it's documentation:</p> <pre><code>RAND() is not meant to be a perfect random generator. It is a fast way to generate random numbers on demand that is portable between platforms for the same MySQL version. </code></pre> <p>i.e. the code for it is questionable in being a true random number generator - it's good enough for most purposes, but can't be trusted for use in, say, encryption, and I'd wager can't be trusted to even be as uniform as you may expect.</p> <p>Their claim that it's not perfect means it will almost certainly fail at least some of these tests; the how is still unclear, but if it's not a perfect RNG, you won't see a perfectly uniform distribution; I'd expect either gaps or peaks of ranges that are more/less common. <a href="http://www.stat.fsu.edu/pub/diehard/cdrom/pscript/monkey.ps" rel="nofollow">http://www.stat.fsu.edu/pub/diehard/cdrom/pscript/monkey.ps</a> (there's been other work since but this is still some of the key work in validating RNG's).</p> <p>It'd wager that code behind it certainly does <em>not</em> try to guarantee a uniform distribution, since to do so (track history of what's come up already) would waste masses of memory. In any case, if you've already generated a lot of values using a perfect RNG, nothing guarantees that if your values so far were all low the next one will be high. It will always be just as random..</p>
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