LEFT JOIN给出不正确的总和结果

Question

我有两个表上（daily_book和extra_cost），这样的结构是

daily_book

db_id | refund     
1  | 7161     
2  | 5980     

extra_cost

ec_id | db_id | cost 
1  | 1  | 156 
2  | 1  | 123 
3  | 2  | 100 
4  | 2  | 120 

所以我得到总退款金额和总成本值。

所以我的查询是

$sql = "SELECT SUM(d.refund) AS refund, SUM(e.cost) AS e_cost FROM `daily_book` d LEFT JOIN extra_cost e ON (d.db_id = e.db_id) WHERE d.db_id > 0"; 

我得到的结果是26282退款和499的总成本;这是不正确的。

我想要的结果是13,141退款和499总成本。

Answer 1

这里没有神秘感。您正在汇总多行的退款。你需要分别做聚合。在MySQL中，这是有点麻烦，但这里有一个方法：

SELECT dd.refund, SUM(e.cost) AS e_cost 
FROM daily_book d LEFT JOIN 
    extra_cost e 
    ON (d.db_id = e.db_id) CROSS JOIN 
    (SELECT SUM(d.refund) as refund FROM daily_book d WHERE d.db_id > 0) dd 
WHERE d.db_id > 0;