选择带有减号和总和的查询

Question

有 3 个表：user、project 和 tracking。这是tracking的表格：

id	user_id	project_id	start_time	end_time
123	32	12	8	12
124	32	12	13	17
125	77	63	10	11
126	77	12	13	17
127	15	12	15	17
128	24	12	8	10

start_time 和 end_time 字段与工作时间相关（8 到 12、13 到 17）。 当然，每天，用户都可以为许多项目做出贡献。

现在我想获取项目信息如下：

Project name	Total tracking time
First	1860
Second	3122

其中，Total tracking time 是项目成员被跟踪为贡献者的所有时间的总和。

如何通过select 查询获得此结果？以下不起作用。

SELECT *,
  SUM(SELECT *, (end_time - start_time) AS tracking_time,
    FROM tracking
    WHERE project_id = project.id
  )) AS tracking_time,
FROM project

Answer 1

您的查询应该是这样的：

SELECT p.*, t.tracking_time
FROM project p
JOIN (
  SELECT project_id, SUM(end_time - start_time) AS tracking_time
  FROM tracking
  GROUP BY project_id
) t ON p.project_id = t.project_id

或者，您尝试过的更正查询也可以：

SELECT *,
  (SELECT SUM(end_time - start_time) AS tracking_time
   FROM tracking
   WHERE project_id = project.id
  ) AS tracking_time
FROM project

Answer 2

假设project表的列名，我认为以下查询可以提供帮助：

SELECT 
    name as 'Project name', 
    SUM(end_time - start_time) as 'Total tracking time'
FROM project p JOIN tracking t
ON p.id = t.project_id
GROUP BY name