title: How do I multiply the arrays (as SQL does)
body: <p>Let's say I have several arrays:</p>
  
  <pre><code>$array1 = array( 'a','b','c');
  $array2 = array( '1','2','3');
  $array3 = array( '+','-');
  </code></pre>
  
  <p>As a result I'd like to have a array of all possible mixes of those arrays:</p>
  
  <pre><code>$result = array( 'a1+','a1-','a2+','a2-','b1+','b1-','b2+'...
  </code></pre>
  
  <p>SQL provides such operation in case of the following request:</p>
  
  <pre><code>SELECT * FROM `letters`,`digits`,`operations`
  </code></pre>
  
  <p>Ho can I do this in PHP?</p>