SQL通过联结表从其他表中选择总和作为列

Posted 2023-05-08

【中文标题】SQL通过联结表从其他表中选择总和作为列

【英文标题】：SQL select sum from other table as a column via junction table

【发布时间】：2009-08-01 15:51:16

【问题描述】：

我有 2 个常规表“Tasks”和“Employees”和一个连接表 EmployeeTasks，它们看起来像这样

任务

任务 ID 项目ID 持续时间

员工

员工 ID 员工姓名

员工任务

员工 ID 任务 ID

我正在尝试找到一个 tsql 查询，该查询基于通用项目 ID 将提供每个员工花费的总时间和完成的任务数量的摘要。类似这样：

"Employee" | "Number of Tasks" | "Time Spent"
----------------------------------------
John       |        5          |  123
Sam        |        4          |   72

【问题讨论】：

没有零，谢谢！呵呵，没有作业我只是通常不使用数据库，并且正在努力了解 SQL。

【参考方案1】：

SELECT E.EmployeeName, COUNT(T.TaskID) AS [Number of Tasks], SUM(T.Duration) as [Time Spent]
FROM Employee E, EmployeeTasks ET, Tasks T
WHERE ET.EmployeeID = E.EmployeeID AND ET.TaskID = T.TaskID
GROUP BY E.EmployeeName

【参考方案2】：

试试这个：

 Select EmployeeName, 
      Count(et.TaskId) NumTasks,
      Sum(T.Duration) TimeSpent
  From Employees E
     Left Join (EmployeeTasks eT Join Tasks T 
                   On T.TaskId = eT.TaskId)
        On eT.EmployeeId = E.EmployeeId 
  Where ProjectId = @ProjectId
  Group By EmployeeName

这将适用于所有员工-项目组合

  Select EmployeeName, ProjectId, 
      Count(et.TaskId) NumTasks,
      Sum(T.Duration) TimeSpent
  From Employees E
     Left Join (EmployeeTasks eT Join Tasks T 
                   On T.TaskId = eT.TaskId)
        On eT.EmployeeId = E.EmployeeId 
  Group By EmployeeName, ProjectId

【参考方案3】：

请注意，如果您需要为没有任务的员工显示时间，这会有所不同。

SELECT Count(TaskID) as NumOfTasks, Sum(Duration) as TimeSpent
FROM Employee 
INNER JOIN EmployeeTasks on Employee.EmployeeID = Tasks.EmployeeID
INNER JOIN Tasks on EmployeeTasks.TaskID = Tasks.TaskID
WHERE ProjectID = @ProjectID
GROUP BY EmployeeID

如果您想要员工姓名，您可以将其作为子选择加入

SELECT EmployeeName, NumOfTasks, TimeSpent
FROM Employees 
INNER JOIN (insert select here) TaskSummary on Employees.EmployeeID = TaskSummary.EmployeeID