title: Merge Date and Time into one variable in php
body: <p>I have got 2 variables like:</p>
  
  <pre><code>$date //2011-01-01
  $full_old_date //1999-01-01 12:00:00
  </code></pre>
  
  <p>Now I want to combine the new date and the time of the $full_old_date together as a new variable like:</p>
  
  <pre><code>$full_new_date //2011-01-01 12:00:00
  </code></pre>
  
  <p>What should I do to extract only the time from the old one and combine them together as a new date variable?</p>