从特定用户的两个mysql表中获取数据

Question

SELECT customer_id,created,total_price 
FROM `orders` 
UNION SELECT product_id,quantity 
FROM order_items

我的代码是从特定用户的两个mysql表中获取数据。

Answer 1

使用UNION时必须等于列数，如果数量为null，则可以添加IFNULL

    $query = "SELECT `product_id`, `total_price`, ‌`​‌​created`, IFNULL(`quantity`,0) FROM `order_items`
    LEFT JOIN `orders` ON `order_items`.`order_id` = `orders`.`id`
    WHERE `orders`.`customer_id`={$_SESSION['email']}");
    $order_result = mysqli_query($conn, $query);

PS：为了准确回复，请粘贴表格架构

Answer 2

假设order_id是order_items表中的forein键列，您可以使用JOIN和COUNT来获取所需的值，例如：

SELECT o.customer_id, o.created, o.total_price, COUNT(oi.id)
FROM orders o LEFT JOIN order_items oi ON o.id = oi.order_id
GROUP BY o.customer_id, o.created, o.total_price;