乘兩列的值

Question

我有2個表客戶和牛奶如下圖所示

客戶

customers (cid, name, price); 

牛奶

milk (mid, customer_id, milk_letters, mprice) 

我想將價格乘以milk_letters和store在mprice where customer_id = cid

我想

$cid = $_POST['cid']; 
$milk_letters = $_POST['milk_letters']; 
$sql = "INSERT INTO milk (customer_id, milk_letters, milk_date) 
     VALUES ('$cid','$milk_letters', NOW())"; 
dbQuery($sql); 
$sql2 = "INSERT INTO milk SELECT SUM(price * milk_letters) as mprice FROM customers , milk WHERE customers.cid = '$cid' and milk.customer_id = '$cid'"; 
    $result2 = dbQuery($sql2); 

Answer 1

你可以在一個查詢，而不是2

INSERT INTO milk (customer_id, milk_letters, milk_date, mprice) 
SELECT {$cid}, {$milk_letters}, NOW(), customers.price * {$milk_letters} 
FROM customers 
WHERE customers.cid = {$cid}