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copied!<p>First of all, the direct error in your code is</p> <pre><code>if(mysql_num_rows($result) == 1) { $rrezervim_id = rand(1, 5); } </code></pre> <p>fails, if you hit a taken number <strong>twice</strong>. You need a loop, such as </p> <pre><code>while (mysql_num_rows($result) == 1) { $rrezervim_id = rand(1, 5); $result = mysql_query("SELECT rrezervim_id FROM pax_list WHERE rrezervim_id='$rrezervim_id'"); } </code></pre> <p>That said, I suspect, that there is more wrong with your code:</p> <ol> <li><p>If you want to use this "free" random number to insert it into the database at a later point in time, you are wide open to a race condition: Both processes select the same (still free) number, but only on the first insert is it still unique. </p></li> <li><p>This approach can have extremely bad performance, if your field of possible random numbers is nearly full: If you have 80% fill rate, such as in your example, you will on average have 4 "bad" hits, before getting a "good" hit.</p></li> </ol> <p>I recommend you consider using a database built-in, such as the battle-proven AUTO_INCREMENT as a primary means, then use a formula to create the hard-to-guess pseudo-random from it. <a href="http://en.wikipedia.org/wiki/LFSR" rel="nofollow">A linear feedback shift register</a> can be one approach, while cryptographically combining the auto-generated ID and a (not necessarily unique) pseudo-random stored in the table might be another. Both methods give you linear performance and race-free usage.</p>

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