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    <p>This sounds like an urban legend to me.</p> <p><code>bin2hex()</code> maps each byte in the input to <em>two</em> bytes in the output (<code>'a'</code> -> <code>'61'</code>), so you should notice a significant memory increase of the script performing the query - it should use at least as much memory more as the byte length of the binary data to be inserted.</p> <p>Furthermore, this implies that running <code>bin2hex()</code> on a long string takes <em>much</em> longer than running <code>mysql_real_escape string()</code>, which - as explained in <a href="http://dev.mysql.com/doc/refman/5.0/en/mysql-real-escape-string.html" rel="noreferrer">MySQL's documentation</a> - just escapes 6 characters: <code>NULL</code>, <code>\r</code>, <code>\n</code>, <code>\</code>, <code>,</code> and 'Control-Z'.</p> <p>That was for the PHP part, now for MySQL: The server needs to do the reverse operation to store the data correctly. Reversing either of the functions takes almost as long as the original operation - the reverse function of <code>mysql_real_escape_string()</code> needs to replace escaped values (<code>\\</code>) with unescaped ones (<code>\</code>), whereas the reverse of <code>bin2hex()</code> would need to replace <em>each and every byte tuple</em> with a new byte.</p> <p>Since calling <code>mysql_real_escape_string()</code> on binary data is safe (according to MySQL's and <a href="http://php.net/manual/en/function.mysql-real-escape-string.php" rel="noreferrer">PHP's documentation</a> or even when just considering that the operation does not do any other conversions than the ones listed above), it would make absolutely no sense to perform such a costly operation.</p>
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    1. COThat makes sense. The added memory required to store the query string in PHP alone would seem enough of a reason to avoid the `bin2hex` function, and my own tests indicate that MySQL suffers as well. And then there is the added CPU cost of the conversions. - This is indeed sounding more and more like an urban legend. Still, I have to wonder what got this started; why people think this is a good idea.
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    2. COI would think some people thought it might be unwise to encode binary data with a function called `..._escape_string` or to send binary data within a human-readable SQL statement, but there is actually nothing wrong with that (although there could have been an alias for the function - like `mysql_escape_data()` or similar)
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    3. COGood points. I can see how people might look at it that way, especially those coming from strongly-typed languages. - I never really considered them all that different, though. I mean, PHP strings are basically just byte arrays, just like the binary data. (Until PHP 6, at least.)
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