2個SQL表的組合

Question

我有下表（簡化后）：

 CUSTOMERS
 -int id
 -varchar name

 ENVENTS
 -int id
 -int customer_id
 -int duration

我的問題是，我想獲取具有相同customer_id的持續時間總和，然后用表客戶的名稱替換customer_id。

所以輸出應該是：

+--------------+----------------+
| name         | sum(durtaions) |
+--------------+----------------+
| customername |          12313 |
+--------------+----------------+

• 那只是一個例子。

有人可以給我提示嗎？

Answer 1

嘗試連接兩個表並使用GROUP BY子句來實現此目的：

SELECT c.name
      ,SUM(e.duration) AS duration
  FROM Customers c 
  JOIN EVENTS e 
    ON c.id = e.customer_id
 GROUP BY c.id

參見此示例SQLFiddle

---

編輯：

如果客戶不在事件表中，請嘗試使用LEFT JOIN獲取持續時間為0的客戶名稱

SELECT c.name
      ,IFNULL(SUM(e.duration),0) AS duration
  FROM Customers c 
  LEFT JOIN EVENTS e 
    ON c.id = e.customer_id
 GROUP BY c.id

看到這個SQLFiddle

看看MySQL中的JOIN和SQL連接的可視化解釋

Answer 2

請嘗試以下代碼。

select c.name,SUM(e.duaration) as duration 
from customer as c 
left join events as e 
    on c.id = e.id 
group by e.customer_id