title: PHP variables as MySQL record
body: <p>In my PHP file, a have these variables:
  <code>$a</code>, <code>$b</code>, <code>$c</code> and <code>$d</code>.</p>
  
  <p>Depending on the mode a user selects, a different formula should be used to calculate a certain number. I would like to store these formulas in a MySQL database:</p>
  
  <pre><code>ID      /      Mode      /      Formula
  
  mode1      namemode1        $a*$b/$c+$d
  mode2      namemode2    /   $a/$b+$c+$d
  etc.
  </code></pre>
  
  <p>How could I make the string I get when I select it from the database into PHP variables? Is there sort of a best practice for this?</p>