SUM行與條件

Question

的SQL Statment我已經user_id = 23，我要查詢，我也有一個表work_log包括project_id，user_id，log_hours這樣的：

+----+------------+---------+-----------+ 
| id | project_id | user_id | log_hours | 
+----+------------+---------+-----------+ 
| 1 | 23  | 23 | 2.5  | 
| 1 | 3  | 23 | 3  | 
| 1 | 23  | 23 | 1  | 
| 1 | 24  | 23 | 3  | 
| 1 | 24  | 23 | 1.5  | 
| 1 | 23  | 23 | 0.5  | 
+----+------------+---------+-----------+ 

但現在我要總結所有log_hours對於每個結果有：

+------------+------------------+ 
| project_id | sum_of_log_hours | 
+------------+------------------+ 
|  23  |  4   | 
|  3  |  3   | 
|  24  |  4.5  | 
+------------+------------------+ 

我如何寫SQL語句有結果？

Answer 1

這應做到：

Select project_id, sum(log_hours) as sum_log_hours 
from work_log 
where user_id = '23' 
group by project_id 

Answer 2

要顯示與和所有的記錄，只是簡單地去掉where條件。

SELECT project_id, sum(log_hours) AS sum_log_hours 
    FROM work_log GROUP BY project_id