Mysql LEFT JOIN 和 SUM 并显示 0 而不是 NULL

Question

我有第一个表名为“orders”，第二个表名为“details”

orders :
order_id
1
2
3

details :
id | order_id | qty
1  |  1       | 2
2  |  1       | 3

如何显示如下？

order_id | total
1        | 5
2        | 0
3        | 0

我试过这个查询但没有成功:

SELECT *, SUM(qty) AS total
FROM order o
LEFT JOIN details d
  ON o.order_id = d.order_id

Answer 1

试试这个:

SELECT o.order_id, IFNULL(SUM(d.qty),0) AS total
FROM orders o
    LEFT JOIN details d ON o.order_id = d.order_id
 GROUP BY order_id