根据示例表，您似乎希望分组
product而不是
id。您只需要将
Size列添加到
SELECt列表和
GROUP BY
$query = "SELECT product, Size, SUM(Quantity) AS TotalQuantityFROM inventory GROUP BY product, Size";
请注意，我添加了一个列别名
TotalQuantity，这将让您更轻松地通过更明智的检索所取得的行的列
$row['TotalQuantity']，而不是
$row['SUM(Quantity)']
