SQL通過聯結表從其他表中選擇總和作為列

Question

我有兩個常規表“ Tasks”和“ Employees”，還有一個聯結表EmployeeTasks簡化了，它們看起來像這樣

任務

• 的TaskID
• 專案編號
• 持續時間

雇員

• 員工ID
• 員工姓名

EmployeeTasks

• 員工ID
• 的TaskID

我試圖找到一個基於通用項目ID的tsql查詢，該查詢將提供總花費時間和每個員工完成的任務數量的摘要。 與此類似：

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

Answer 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

Answer 2

嘗試這個：

 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

這將適用於所有員工-項目組合

  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

Answer 3

請注意，如果您需要為沒有任務的員工顯示時間，則這是不同的。

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

如果您想要員工姓名，則可以將其作為子選擇加入

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