表更新触发器触发的行数超过更新的行数

Question

我有一个触发器，它应该在更新设置为 ON 的 Employees 表时将新记录插入审计历史表 (EmployeeSalaryHistory)。

如果我在Employees 上执行UPDATE，其中表中的所有行都已更新，则调用触发器的次数多于正在更新的行数。

例如如果Employees 表中有三行，INSERT 会发生 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

这个查询本质上是一个“交叉连接”

inserted I, deleted D

3 x 3

注意，如果我运行此查询...

Use Northwind
GO

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

我得到“x 平方”作为返回的行数，其中 x 是 [dbo].[Categories] 表中的行数。

编辑

试试这个

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 */

回到通用示例：

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

将有“x 行”，而不是“x 平方行”......