具有內部選擇的MYSQL SUM返回最大日期

Question

我正在嘗試提出一個查詢，該查詢將使用下表（名為sales ）：

user_id  |  order_total   |   order_date  |
    1    |      100       |  2012-01-01   |
    1    |      200       |  2013-06-04   |
    1    |      150       |  2012-01-08   |
    2    |      100       |  2015-02-01   |
    3    |      105       |  2014-10-27   |

並將返回以下內容：

user_id  |  order_total   |   num_orders  |  last_order  |
    1    |      450       |     3         | 2013-06-04   |
    3    |      105       |     1         | 2014-10-27   |
    2    |      100       |     1         | 2015-02-01   |

到目前為止，我想出了以下SQL來獲取結果：

SELECT 
DISTINCT a.user_id,
SUM(order_total) AS order_total,
COUNT(*) AS num_orders,
b.order_date as last_order
FROM 
    `sales` AS a,
     (
        SELECT 
        order_date, 
        user_id
        FROM `sales` 
        ORDER BY order_date DESC
      ) AS b
WHERE a.user_id = b.user_id
GROUP BY user_id
ORDER BY order_total DESC

但是，問題在於它返回：

user_id  |  order_total   |   num_orders  |  last_order  |
    1    |      1350      |     9         | 2013-06-04   |
    3    |      105       |     1         | 2014-10-27   |
    2    |      100       |     1         | 2015-02-01   |

有什么方法可以防止子查詢影響Sum和Count的結果嗎？ 還是我走錯路了？

Answer 1

為什么使用子選擇？

SELECT user_id, 
SUM(order_total) AS order_total, 
MAX(order_date) AS lastOrder, 
COUNT(*) AS num_orders 
FROM table 
GROUP BY user_id
ORDER BY order_total DESC