Asp.net 基于辅助表中的行更新主表

我有一个employee draw类型的应用程序，表如下所示：

Employee (ID, name, selectionCount)

Selections (employeeID, ipAddress)

---

现在，我需要一个更新查询，该查询将计算每个employeeID（具有唯一的IPAddress）的选择数，并更新表Employee中的selectionCount列。

不是SQL Server专家，但类似的操作应该可以：

update Employee a
   set selectionCount = (select count(*)
                           from Selections
                          where employeeID = a.ID)

WITH SelectionCounts(EmployeeId, SelectionCount)
AS
(
    SELECT s.EmployeeId, COUNT(DISTINCT IpAddress) AS SelectionCount
    FROM Selections s
    GROUP BY s.EmployeeId
)
UPDATE Employee
SET SelectionCount = sc.SelectionCount
FROM SelectionCounts sc
WHERE ID = sc.EmployeeId

---

顺便说一句，我想你知道设计有点非规范化，这在某些情况下可能是不可取的。

类似的方法应该可以：

update Employee a
   set selectionCount = (select count(*)
                           from Selections
                          where employeeID = a.ID)

WITH SelectionCounts(EmployeeId, SelectionCount)
AS
(
    SELECT s.EmployeeId, COUNT(DISTINCT IpAddress) AS SelectionCount
    FROM Selections s
    GROUP BY s.EmployeeId
)
UPDATE Employee
SET SelectionCount = sc.SelectionCount
FROM SelectionCounts sc
WHERE ID = sc.EmployeeId

---

未对其进行测试，因此语法可能不完全正确。

采用najmeddine解决方案后，您可以将该代码放入SQL Server中Selections表的insert和/或update触发器中：

update Employee
set selectionCount = (select count(distinct ipAddress) 
                        from Selections 
                       where Selections.emmployeeID = Employee.ID)

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE TRIGGER UpdateSelectionCount ON Selections
    AFTER UPDATE, INSERT
AS
BEGIN
    SET NOCOUNT ON

    UPDATE
        Employee
    SET
        selectionCount = (SELECT
                              COUNT(DISTINCT ipAddress)
                          FROM
                              Selections
                          WHERE
                              Selections.EmployeeID = Employee.ID)

END
GO