Сергей Анисимов

<input type="hidden" name="l" value="'.$order_id.'">

<input type="hidden" name="l" value="<?php echo $order_id ?>">

$displayA = $displayB = $displayC = false;

foreach ($res as $row) {
    if ($displayA && $displayB && $displayC) {
        break;
    }
    if ($row['a'] > 0) {
        $displayA = true;
    }
    if ($row['b'] > 0) {
        $displayB = true;
    }
    if ($row['c'] > 0) {
        $displayC = true;
    }
}

echo '<table class="table" style="max-width: 100%; min-width: 75%;"><thead><tr><td>Наименование</td>';
if ($displayA) {
    echo '<td>A</td>';
}
if ($displayB) {
    echo '<td>B</td>';
}
if ($displayC) {
    echo '<td>C</td>';
}
echo '<td>Цена</td></thead><tbody>';

foreach ($res as $row) {
    echo '<tr>';
    echo '<td>' . $row['item-name'] . '</td>';
    if ($displayA) {
        echo '<td>' . $row['a'] . '</td>';
    }
    if ($displayB) {
        echo '<td>' . $row['b'] . '</td>';
    }
    if ($displayC) {
        echo '<td>' . $row['c'] . '</td>';
    }
    echo '<td>' . $row['price-rozn'] . '</td>';
    echo '<tr>';
}