sql server 触发器 trigger

做增删改操作时自动触发另一个操作。

触发器分类

1. instead of 触发器：在执行操作之前被执行。
2. after触发器：在执行操作之后被执行。

举例：

部门表 Department：

员工表 People:

1、假设有部门表和员工表，在添加员工的时候，该员工部门编号在部门表中找不到，则自动添加部门信息，部门名称为“新部门”。

create trigger tri_InsertPeople on People after insert
as
    if not exists(select * from Department where DepartmentId = (select DepartmentId from inserted) )
        begin
            insert into Department(DepartmentId,DepartmentName) values ((select DepartmentId from inserted), '新部门')
        end
go

• tri_InsertPeople ：触发器名
• after insert：在插入之后触发
• inserted：临时表的名字

2、删除一个部门的时候，将部门下的所有员工删除

create trigger tri_DeleteDept on Department after delete
as
    delete from People where DepartmentId = (select DepartmentId from deleted)
go

3、删除一个部门的时候，判断该部门下是否有员工，有则不删除，没有则删除。

create trigger tri_DeleteDept on Department instead of delete
as
    if not exists(select * from People where DepartmentId = (select DepartmentId from deleted) )
        delete from Department where DepartmentId = (select DepartmentId from deleted)
go

4、修改一个部门编号后，将该部门下所有员工的部门编号同步修改。

create trigger tri_UpdateDept on Department after update
as
    update People set DepartmentId = (select DepartmentId from inserted)
    where DepartmentId = (select DepartmentId from deleted)
go