Question

我需要获得订单数量的客户列表。实际上使用下面的查询来获得客户的订单，如：

+-------+----------------+
| JAMES | 2 orders total |
| PAUL  | 6 orders total |
+-------+----------------+

为此，我使用此查询：

SELECT *
FROM mod_users    
INNER JOIN (SELECT order_user_id, count(*) as order_qty
            FROM mod_orders
            GROUP BY user_order_id) AS order_qty
  ON mod_users.user_id = order_qty.order_user_id;

现在，我想让用户没有订单：

+-------+----------------+
| JAMES | 2 orders total |
| PAUL  | 6 orders total |
| FRANK | 0 orders total |
+-------+----------------+

任何人都可以帮忙进行查询吗？

Answer 1

使用LEFT JOIN代替INNER JOIN：

SELECT mod_users.user_id, COALESCE(order_qty, 0) AS ordersCount
FROM mod_users    
LEFT JOIN (SELECT order_user_id, count(*) as order_qty
            FROM mod_orders
            GROUP BY user_order_id) AS order_qty
  ON mod_users.user_id = order_qty.order_user_id;

如果mod_orders未包含特定用户的任何记录，则order_qty对于此用户NULL将归LEFT JOIN。 COALESCE将此NULL值转换为0。

没有订单的客户

1 个答案: