php - How to select DISTINCT using WHERE and OR -

i new php , have searched google, other forums, web site , looked @ several books cannot see how this. please not castigate me ignorance. want select distinct entries field (category) based on criteria field (code) , display drop down list containing distinct categories. field named 'code' contains 1 of 3 data values, being 1, 2, or 4. want select distinct category if code field has '2' or '4', not if contains value '1'.

i have tried several ways of doing confirmation database connection worked drop down box below has no content.

my current code after many trials is:

if ( ! $_post['submit'] )     {         // form not submitted, display form input user          echo '<form method="post" id="form_id" action="' . htmlspecialchars($_server["php_self"]) . '">';         try {         $dbh = new pdo("mysql:host=$hostname;dbname=gosdirect", $username, $password);         $code2 = '2';         $code4 = '4';         $sql = $dbh->prepare("select distinct category directory code =$code2 or code =$ode4     order category asc");         $sql->execute();         // display message if connection ok         echo ' connected database<br />';         echo 'i looking local: <select name="category">';         while ($row = $sql->fetch(pdo::fetch_assoc))         {         $category = $row['category'];         echo '<option value="' . $category . '">' . $category . '</option>';         }         echo '</select>';         // close database connection         $dbh = null;         }         catch(pdoexception $e)         {         echo $e->getmessage();         }         echo '<input id="form_submit" type="submit" name="submit" value="search" /></form>';         ?> 

if use line:

$sql = $dbh->prepare("select distinct category directory order category asc"); 

i drop down box populated category names, includes categories have value of '1' in 'code' field , don't want that, assuming there fundamentally wrong 'select request.

here image of get:

screen shot http://www.wigweb.biz/gosport-error.jpg

i appreciate on this.

many thanks

tog porter

it matches codes have 2 or 4 in , exclude have 1 in them

select distinct category  directory  (code '%2%' or code '%4%') , not  (code '%1%') order category asc 

also if want use variable in sql varchar filed surround quote '$code2'