添加一列的值并插入不同的表mysql

Question

我有2个表顾客和牛奶，如下所示

客户

customers (cid, name, price, total);

乳

milk (mid, customer_id, milk_letters, mprice)

我正在尝试

$cid = $_POST['cid'];

我想将客户表更新为牛奶的总和（mprice），其中customer_id = cid

Answer 1

sql代码：

UPDATE customers c
SET total=(SELECT SUM(mprice) FROM milk WHERE customer_id=c.cid)
WHERE c.cid=$cid

也使用intval

$cid = intval($_POST['cid']);