title: MySQL query with conditional statement?
body: <p>I have a MySQL query left joining two tables. This is the current query result:</p>
  
  <pre><code>id | login | privacy-weight | requires
  --------------------------------------------
  0  | user  | 1              | NULL
  0  | user2 | 1              | NULL
  0  | user3 | 1              | privacy-weight
  </code></pre>
  
  <p>The query itself is not important, as I'd only like to add a <code>WHERE</code> condition to the query as it is now.</p>
  
  <p>I need to fetch only values which (in my own words):</p>
  
  <pre><code>IF (`requires` = 'privacy-weight'), then `privacy-weight` must equal = 0;
  </code></pre>
  
  <p>That means, I need this condition:</p>
  
  <pre><code>WHERE `privacy-weight` = 0
  </code></pre>
  
  <p>BUT only if this is true:</p>
  
  <pre><code>requires = 'privacy-weight'
  </code></pre>
  
  <p>Can this be done?</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>Obviously this is too difficult to understand, therefore, an example output:</p>
  
  <pre><code>privacy-weight | requires
  -------------------------
  0              | NULL
  1              | NULL
  0              | privacy-weight
  1              | NULL
  </code></pre>
  
  <p>These would be ignored (not fetched):</p>
  
  <pre><code>privacy-weight | requires
  -------------------------
  1              | privacy-weight
  </code></pre>