根據輔助表中的行更新主表

Question

我有一個員工抽獎類型的應用程序，表格如下所示：

Employee (ID, name, selectionCount)

Selections (employeeID, ipAddress)

現在，我需要一個更新查詢，該查詢將計算每個employeeID（具有唯一的IP地址）的選擇數量，並更新表Employee中的selectionCount列。

Answer 1

這樣的事情應該起作用：

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

沒有測試它，因此語法可能不完全正確。

Answer 2

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

Answer 3

使用najmeddine解決方案，您可以將該代碼放入SQL Server中Selections表的插入和/或更新觸發器中：

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

Answer 4

不是SQL Server專家，但是這樣的方法應該起作用：

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

順便說一句，我想您知道設計有些不規范，這在某些情況下可能是不希望的。