title: MYSQL variable IN clause
body: <p>In filtering out some spam, I have two MYSQL statements in one file, </p>
  
  <pre><code>SET @valid_users := '"admin", "jrock", "kmicka", "First Last"';  //etc
  </code></pre>
  
  <p>Followed by a SELECT like this</p>
  
  <pre><code>SELECT /*stuff*/ /*WHERE*/ /*filters*/ AND User.user_name NOT IN (@valid_users)
  </code></pre>
  
  <p>When I do this, it acts as if <code>@valid_users</code> is an empty string. (Returns all results).  But if I change the clause to <code>NOT IN ('admin', 'jrock', etc)</code> then it works as it should.</p>
  
  <p>Why would a variable in the <code>NOT IN</code> filter not work?</p>