I am trying to get a select box with optgroup to populate from a MySQL database. The problem is I can't see how to get the WHERE clause to work.

Here is an example of the code I am using. Currently it displays the optgroups correctly (these are manufacturers) but it lists all cars.

How can I add a WHERE clause to get only cars that match the manufacturer to appear under the optgroup.

<select>
  <?php
	$manufacturer  = mysql_query("SELECT * FROM cars");
	while($manufacturer_row = mysql_fetch_array($manufacturer )){
    echo "<optgroup label='$manufacturer_row[manufacturer]'>"; 

	$car = mysql_query("SELECT * FROM cars");
	 
	while($car_row = mysql_fetch_array($car)){
    echo "<option>$car_row[car]</option>"; 
	}
	}
  ?>
</optgroup>
</select>

Use an "ORDER BY" criteria in your query and check when the "manufacturer" column data changes, then insert your optgroup.

How do you check for changes in a column?

So, you want to list all cars under their respective manufacturer?

PHP Code:

// run your query, something like
// "select manufacturer, car from cars order by manufacturer"

// manufacturer of the previous car
$previous = "";

// just a little help variable
$first_car = true;

while($row = mysql_fetch_array($manufacturer)) {

    // if this car is of another manufacturer than the last one,
    // add a new optgroup
    if ($row['manufacturer'] != $previous) {
        if (!$first_car) {
            echo '</optgroup>';
        } else {
            first_car = false;
        }
        echo '<optgroup label="' . $row['manufacturer'] . '">';
        $previous = $row['manufacturer'];
    }

    // print the current car
    echo '<option>' . $row['car'] . '</option>';

}
// close the last optgroup tag
echo '</optgroup>'; 


Thanks that works - but I need to add OrderBy to both elements (the car and the manufacturer) to ensure they stay in order.

When I do this I get duplicate groups.

You mean like this?
"select manufacturer, car from cars order by manufacturer, cars"

thanks - thats done it!