php - 分组后的mysql总和

Question

购物车表:

itemid | amount 
------ | ------
1      | 2
2      | 4 

产品表:

itemid | Price
------ | ------
1      | 10
2      | 20

到目前为止我已经尝试过:

$cartPrice = 
"SELECT (SUM(products.Price) * SUM(cart.amount)) 
AS total_price 
FROM cart 
INNER JOIN products 
ON cart.itemid = products.itemid 
WHERE userid = '$IP' 
GROUP BY cart.itemid";

$Price = $mysqli->query($cartPrice);
$rowPrice = $Price->fetch_assoc();

echo "Total: ". $rowPrice['total_price'] ." ";

我的 MYSQL 查询输出如下:

total_price |
----------- | 
20          | 
80          | 

它将回显最后的结果。但是我需要总数为 80 + 20。我该怎么做？

我现在得到的结果:

Total: 80

我想要的结果:

Total: 100

谢谢

Answer 1

您不必 GROUP BY 因为您只想返回一行:

SELECT SUM(products.Price* cart.amount) AS total_price 
FROM cart 
INNER JOIN products 
ON cart.itemid = products.itemid 
WHERE userid = '$IP'