title: Multiple selection if some form option are selected
body: <p>I want to make a dynamic filter system based on a html form with multiple options, some like that: <Br></p>
  
  <pre><code>&lt;form&gt;
    &lt;select&gt;
    &lt;option&gt;&lt;/option&gt;
    -//-
    &lt;/select&gt;
    &lt;select&gt;
    &lt;option&gt;&lt;/option&gt;
     --//--
     &lt;/select&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>and make a sql query but with condition from form, and every option have an "All" option which means no condition.
  So i was thinking to make something like that, with multiple for and N^2 if condition, but is to much code and it's not faster... to make 16 if-uri and 16 SELECT for a 4 option form ... <br>
  So, know someone a faster solution ? <BR>
  Thanks.<BR>
  Edit <br >
  So let say i have a database users with ID, Name, Age, City.<br>
  I make a form with 3 option (1 for Name, 1 for Age, 1 for City) so i can see only some users, let say i want all users which have name Nick and it's from Miami.<BR>
  I need to my SELECT condition to exclude the condition for AGE, like now select will be :<br><code>Select * from Users where Name = 'Nick' and City='Miami'</code><br>, but if i want to see users with Age= 18 and City NY my select will need to exclude the condition for Name, and be like:<br> <code>Select * from Users where Age= 18 and City='NY'</code>.</p>