On Thu, 2005-08-04 at 15:00 -0400, Scott Hamm wrote: > I've noticed that rand() do not change on each query request. Is there a way > I could get a TRUE randominess into MySQL?
http://dev.mysql.com/doc/mysql/en/mathematical-functions.html Are you using RAND() or RAND(n)? Using RAND() makes MySQL choose its own seed (the documentation doesn't specify what seed it will use). If you choose to seed the random number generator (for example, RAND(3)) and then start using RAND() it will produce a repeatable sequence. mysql> SELECT rand(3), rand(), rand(); +------------------+------------------+------------------+ | rand(3) | rand() | rand() | +------------------+------------------+------------------+ | 0.18109050875631 | 0.75023213843837 | 0.20788919665654 | +------------------+------------------+------------------+ 1 row in set (0.00 sec) mysql> SELECT rand(), rand(), rand(); +------------------+------------------+------------------+ | rand() | rand() | rand() | +------------------+------------------+------------------+ | 0.78874959870125 | 0.32008043427028 | 0.23415340598128 | +------------------+------------------+------------------+ 1 row in set (0.01 sec) mysql> SELECT rand(3), rand(), rand(); +------------------+------------------+------------------+ | rand(3) | rand() | rand() | +------------------+------------------+------------------+ | 0.18109050875631 | 0.75023213843837 | 0.20788919665654 | +------------------+------------------+------------------+ 1 row in set (0.00 sec) Notice that the numbers after calling RAND(3) are in the same sequence. However, in answer to your question, there is no way to get TRUE randomness in a computer system. Even cryptographically secure random number generators can be predicted under absolutely identical circumstances. -- Pat Adams Applications Programmer SYSCO Food Services of Dallas
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