觸發表更新觸發超過更新的行數

Question

我有一個觸發器應該在更新Employees表時將新記錄插入審計歷史記錄表（EmployeeSalaryHistory），觸發器設置爲開啓。

如果我在Employees上執行UPDATE，表中的所有行都被更新，則觸發器被調用的次數會多於正在更新的行數。

例如如果Employees表中有三行，則INSERT發生9次。

/*This UPDATE will cause the trigger to fire more than the number of rows in the Employees table.*/ 
UPDATE Employees SET Salary = Salary * 2 

/* supposed to be fired whenever the salary of an employee is updated */ 
CREATE TRIGGER [dbo].[EmployeesUpdateSalary] ON [dbo].[Employees] 
AFTER UPDATE 
NOT FOR REPLICATION 
AS 
BEGIN 

INSERT INTO EmployeeSalaryHistory(EmployeeID, NewSalary, OldSalary) 
SELECT I.EmployeeID, I.Salary, D.Salary 
From inserted I, deleted D 
WHERE I.Salary <> D.Salary 

END 

Answer 1

你基本上有一個 「交叉聯接」 與此查詢

inserted I, deleted D 

3×3

注意，如果我運行此查詢...

Use Northwind 
GO 

Select * from 
[dbo].[Categories] c1 , [dbo].[Categories] c2 

我得到「x squared」作爲返回的行數，其中x是[dbo]。[Categories]表中的行數。

編輯

試試這個

INSERT INTO EmployeeSalaryHistory(EmployeeID, NewSalary, OldSalary) 
SELECT I.EmployeeID, I.Salary, D.Salary 
From inserted I, deleted D 
where I.EmployeeID = D.EmployeeID /* relationship */ 
and 
I.Salary <> D.Salary /* filter */ 

或者

INSERT INTO EmployeeSalaryHistory(EmployeeID, NewSalary, OldSalary) 
SELECT I.EmployeeID, I.Salary, D.Salary 
From inserted I join deleted D on I.EmployeeID = D.EmployeeID /* relationship */ 
Where 
I.Salary <> D.Salary /* filter */ 

爲了把它帶回通用例如：

Use Northwind 
    GO 
Select * from 
[dbo].[Categories] c1 , [dbo].[Categories] c2 
Where c1.CategoryID = c2.CategoryID 

將有 「×行」，而不是「x平方行」......