Read:
SELECT_a_Column
$sql = "SELECT 'liters' FROM " . $wpdb->prefix . "tfp";
$liters = $wpdb->get_col( $sql );
if( $liters ) {
foreach( $liters as $liter ) {
echo '<option value="' . $liter . '">' . $liter . '</option>';
}
}
Read:
SELECT_a_Column
$sql = "SELECT 'liters' FROM " . $wpdb->prefix . "tfp";
$liters = $wpdb->get_col( $sql );
if( $liters ) {
foreach( $liters as $liter ) {
echo '<option value="' . $liter . '">' . $liter . '</option>';
}
}