Question

我有这个问题：

$sql = "SELECT m.id FROM members m
          LEFT JOIN orders o ON o.user_id = m.id AND
            YEAR(date) = YEAR(CURRENT_DATE - INTERVAL 1 MONTH) AND
            MONTH(date) = MONTH(CURRENT_DATE - INTERVAL 1 MONTH)
          LEFT JOIN transactions t ON t.user_id = o.user_id";

我需要得到Transactions.points的总和，所以我这样做：

$sql = "SELECT m.id, COALESCE(SUM(t.points), 0) AS total_points FROM members m
          LEFT JOIN orders o ON o.user_id = m.id AND
            YEAR(date) = YEAR(CURRENT_DATE - INTERVAL 1 MONTH) AND
            MONTH(date) = MONTH(CURRENT_DATE - INTERVAL 1 MONTH)
          LEFT JOIN transactions t ON t.user_id = o.user_id";

但是当我执行此操作时，我将只获得包含一些事务（和订单）的行。如果没有找到交易，我必须做什么才能获得0作为total_points？

文字说明：我想得到订单（订单表）的积分奖励（来自交易表），订单是在上个月创建的。

谢谢！

Answer 1

获取每位用户的积分总和，并在left join中使用该积分，以便在用户没有交易时获取0。

SELECT m.id, COALESCE(t.total_points, 0) AS total_points
FROM members m
LEFT JOIN orders o ON o.user_id = m.id AND
/* use this instead of functions which prevent indexes on the date column from being used */
o.date >= date '2016-11-01' AND o.date <= date '2016-11-30' 
LEFT JOIN (select user_id, SUM(points) total_points 
           from transactions group by user_id) t ON t.user_id = o.user_id

Answer 2

您需要在查询中添加items.forEach(addItemId)子句，否则您在整个结果集上实际执行GROUP BY。不知道在哪个列上，但在SUM()

上说

m.id

在相关表中获取SUM。如果没有找到，则获得0作为总和

2 个答案: