如何在php mysql中从上一条记录中获取总计

我对此有一个问题：

count this id no 1 = usage/nod
count this id no 2 = (usage[id1]+usage[id2])/(nod[id1]+nod[id2])
count this id no 3 = (usage[id1]+usage[id2]+usage[id3])/(nod[id1]+nod[id2]+nod[id3])

等等

“用法/节点”是数据库中的一个字段

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使用PHP和MySQL如何计算呢？

第一行不应该是

usage[id1]/nod[id1]

？

$total_usage = 0;
$total_nod = 0;

while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    $total_usage += $row['usage'];
    $total_nod += $row['nod'];
    $div = $total_usage/$total_nod;
    echo "count this id no $row[id] = $div\n";
}