This is an easy to use code to select records from MySQL database table and display in dropdown combo box using PHP.

$cn=mysql_connect($db_host,$db_user,$db_password) or die(mysql_error());
mysql_select_db($db_name,$cn) or die(mysql_error());
$sql = "SELECT field_name FROM table_name";
$rs = mysql_query($sql) or die(mysql_error());
echo "<select>";
while($row = mysql_fetch_array($rs)){
echo "<option value='".$row["field_name"]."'>".$row["field_name"]."</option>";
}mysql_free_result($rs);
echo "</select>";