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POWhy do PHP and MySQL unix timestamps diverge on 1983-10-29?
 

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  1. POWhy do PHP and MySQL unix timestamps diverge on 1983-10-29?
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    <p>I've been using PHP's <code>strtotime</code> and MySQL's <code>UNIX_TIMESTAMP</code> functions in my app, to convert dates into timestamps. PHP and MySQL are running on my local machine, and these functions generally return the same result, as I expect them to:</p> <pre><code>$ php &lt;?php echo strtotime("2011-06-02"); ?&gt; 1307001600 mysql&gt; SELECT UNIX_TIMESTAMP("2011-06-02") ts; +------------+ | ts | +------------+ | 1307001600 | +------------+ </code></pre> <p>But, sorta by chance, I happened to notice that when I entered <code>1983-01-01</code> as the date, the results were no longer equal:</p> <pre><code>$ php &lt;?php echo strtotime("1983-01-01"); ?&gt; 410263200 mysql&gt; SELECT UNIX_TIMESTAMP("1983-01-01") ts; +-----------+ | ts | +-----------+ | 410256000 | +-----------+ </code></pre> <p>As you can see, PHP returned 410263200, while MySQL returned 410256000 - a difference of 7200 seconds.</p> <p>This got me curious, and I wanted to know on what date the timestamps were no longer equivalent, so I wrote a little program that starts with today's date (in Y-m-d format), uses PHP's <code>strtotime</code> and MySQL's <code>UNIX_TIMESTAMP</code> and compares the results. It then subtracts 1 day from each value and loops until they're no longer equal. </p> <p>The result:</p> <p><strong>1983-10-29</strong></p> <p>On October 29, 1983, for some reason, <code>strtotime</code> and <code>UNIX_TIMESTAMP</code> return values that differ by 7200 seconds. </p> <p>Any ideas?</p> <p>Thanks for reading.</p>
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    1. COWhat timezone are you in? (`date_default_timezone_get()`)? Wonder if it's some odd calendar change specific to a timezone -- presumably that happened on 30 October 1983.
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      1. USMatt Gibson
    2. COUS/Alaska timezone
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    3. COWhat matt said.
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