從兩個mysql表中爲特定用戶提取數據

Question

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

這是我從兩個mysql表中爲特定用戶獲取數據的代碼。

Answer 1

必須列的數量相等使用UNION並且如果您的數量爲空時，你可以添加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：準確的回覆，請粘貼表模式

Answer 2

假設order_id是order_items表中的forein關鍵列，您可以使用JOIN和COUNT來獲得所需的值，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;