Not sure why you made everything bold now.
Just add a blank option right after starting the select.
<select name="category" id="category">
<option> </option>
For this problem, you need to create your query as a string, only adding the fields which are not empty. You can do it like this, where your posted fields have the name "search[]". You would use prepared statements to avoid SQL injection. I seriously suggest stop using Dreamweaver.
$query = "SELECT field FROM table";
$whereClauses = array();
$whereValues = array();
foreach($_POST['search'] AS $name=>$s){
$s = trim($s);
if(strlen($s)){
$whereClauses[] = "`$name` = ?";
$whereValues[] = $s;
}
}
if(count($whereClauses)){
$query .= " WHERE ".join(" OR ", $whereClauses);
}
//Now your query is $query and your arguments for the prepared statement are $whereValues;