PHP/MYSQL 统计订购最多的产品

Question

用户表：

Order_items 表：

订单表：

$sql[2] = "SELECT p.p_name, o.created, COUNT(oi.id) AS db FROM products AS p
           INNER JOIN order_items AS oi ON oi.product_id = p.id
           INNER JOIN orders AS o ON o.id = oi.order_id
           GROUP BY p.p_name
           ORDER BY db DESC, o.created DESC
           LIMIT 1";

$result3= mysqli_query($conn,$sql[2]) or die(mysqli_error());
if (mysqli_num_rows($result3)>0)
{
    while ($record = mysqli_fetch_array($result3))
    {
        echo $record['p_name']." - ".$record['db']." - ".$record['created']."<br/>";
    }
}

我想计算订购次数最多的产品名称、售出多少产品以及订购该产品的最后日期。在这种情况下，结果如下所示： Barack - 4 - 2016-12-15 09:36:21 但我的 SELECT 只计算 3。有什么想法可以解决吗？

Answer 1

试试这个：

SELECT 
    p.p_name,
    MAX(o.created) AS created,
    COUNT(oi.id) AS db
FROM order_items AS oi
LEFT JOIN orders AS o ON oi.order_id= o.id
INNER JOIN products AS p ON p.id = oi.product_id 
GROUP BY oi.product_id
ORDER BY COUNT(oi.id) DESC
LIMIT 1

更新：
因为在你的表Orders 中没有order_id = 3，所以INNER JOIN 会给你3，如果你想得到4，使用LEFT JOIN。