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  • SQL Server的触发器你了解多少
  • 2022/2/7 13:26:09
  • 触发器是一种特殊类型的存储过程,它不同于之前的我们介绍的存储过程。触发器主要是通过事件进行触发被自动调用执行的。而存储过程可以通过存储过程的名称被调用。

    什么是触发器

    触发器对表进行插入、更新、删除的时候会自动执行的特殊存储过程。触发器一般用在check约束更加复杂的约束上面。触发器和普通的存储过程的区别是:触发器是当对某一个表进行操作。诸如:update、insert、delete这些操作的时候,系统会自动调用执行该表上对应的触发器。sql server 2005中触发器可以分为两类:dml触发器和ddl触发器,其中ddl触发器它们会影响多种数据定义语言语句而激发,这些语句有create、alter、drop语句。

    dml触发器分为:

    1、 after触发器(之后触发)

    a、 insert触发器

    b、 update触发器

    c、 delete触发器

    2、 instead of 触发器 (之前触发)

    其中after触发器要求只有执行某一操作insert、update、delete之后触发器才被触发,且只能定义在表上。而instead of触发器表示并不执行其定义的操作(insert、update、delete)而仅是执行触发器本身。既可以在表上定义instead of触发器,也可以在视图上定义。

    触发器有两个特殊的表:插入表(instered表)和删除表(deleted表)。这两张是逻辑表也是虚表。有系统在内存中创建者两张表,不会存储在数据库中。而且两张表的都是只读的,只能读取数据而不能修改数据。这两张表的结果总是与被改触发器应用的表的结构相同。当触发器完成工作后,这两张表就会被删除。inserted表的数据是插入或是修改后的数据,而deleted表的数据是更新前的或是删除的数据。

    11111111

    1111111

    1111111

    update数据的时候就是先删除表记录,然后增加一条记录。这样在inserted和deleted表就都有update后的数据记录了。注意的是:触发器本身就是一个事务,所以在触发器里面可以对修改数据进行一些特殊的检查。如果不满足可以利用事务回滚,撤销操作。

    创建触发器

    语法

    create trigger tgr_name
    on table_name
    with encrypion –加密触发器
        for update...
    as
        transact-sql

    创建insert类型触发器

    --创建insert插入类型触发器
    if (object_id('tgr_classes_insert', 'tr') is not null)
        drop trigger tgr_classes_insert
    go
    create trigger tgr_classes_insert
    on classes
        for insert --插入触发
    as
        --定义变量
        declare @id int, @name varchar(20), @temp int;
        --在inserted表中查询已经插入记录信息
        select @id = id, @name = name from inserted;
        set @name = @name + convert(varchar, @id);
        set @temp = @id / 2;    
        insert into student values(@name, 18 + @id, @temp, @id);
        print '添加学生成功!';
    go
    --插入数据
    insert into classes values('5班', getdate());
    --查询数据
    select * from classes;
    select * from student order by id;

    insert触发器,会在inserted表中添加一条刚插入的记录。

    创建delete类型触发器

    --delete删除类型触发器
    if (object_id('tgr_classes_delete', 'tr') is not null)
        drop trigger tgr_classes_delete
    go
    create trigger tgr_classes_delete
    on classes
        for delete --删除触发
    as
        print '备份数据中……';    
        if (object_id('classesbackup', 'u') is not null)
            --存在classesbackup,直接插入数据
            insert into classesbackup select name, createdate from deleted;
        else
            --不存在classesbackup创建再插入
            select * into classesbackup from deleted;
        print '备份数据成功!';
    go
    --
    --不显示影响行数
    --set nocount on;
    delete classes where name = '5班';
    --查询数据
    select * from classes;
    select * from classesbackup;

    delete触发器会在删除数据的时候,将刚才删除的数据保存在deleted表中。

    创建update类型触发器

    --update更新类型触发器
    if (object_id('tgr_classes_update', 'tr') is not null)
        drop trigger tgr_classes_update
    go
    create trigger tgr_classes_update
    on classes
        for update
    as
        declare @oldname varchar(20), @newname varchar(20);
        --更新前的数据
        select @oldname = name from deleted;
        if (exists (select * from student where name like '%'+ @oldname + '%'))
            begin
                --更新后的数据
                select @newname = name from inserted;
                update student set name = replace(name, @oldname, @newname) where name like '%'+ @oldname + '%';
                print '级联修改数据成功!';
            end
        else
            print '无需修改student表!';
    go
    --查询数据
    select * from student order by id;
    select * from classes;
    update classes set name = '五班' where name = '5班';

    update触发器会在更新数据后,将更新前的数据保存在deleted表中,更新后的数据保存在inserted表中。

    update更新列级触发器

    if (object_id('tgr_classes_update_column', 'tr') is not null)
        drop trigger tgr_classes_update_column
    go
    create trigger tgr_classes_update_column
    on classes
        for update
    as
        --列级触发器:是否更新了班级创建时间
        if (update(createdate))
        begin
            raiserror('系统提示:班级创建时间不能修改!', 16, 11);
            rollback tran;
        end
    go
    --测试
    select * from student order by id;
    select * from classes;
    update classes set createdate = getdate() where id = 3;
    update classes set name = '四班' where id = 7;

    更新列级触发器可以用update是否判断更新列记录;

    instead of类型触发器

    instead of触发器表示并不执行其定义的操作(insert、update、delete)而仅是执行触发器本身的内容。

    创建语法

    create trigger tgr_name
    on table_name
    with encryption
        instead of update...
    as
        t-sql

    创建instead of触发器

    if (object_id('tgr_classes_inteadof', 'tr') is not null)
        drop trigger tgr_classes_inteadof
    go
    create trigger tgr_classes_inteadof
    on classes
        instead of delete/*, update, insert*/
    as
        declare @id int, @name varchar(20);
        --查询被删除的信息,病赋值
        select @id = id, @name = name from deleted;
        print 'id: ' + convert(varchar, @id) + ', name: ' + @name;
        --先删除student的信息
        delete student where cid = @id;
        --再删除classes的信息
        delete classes where id = @id;
        print '删除[ id: ' + convert(varchar, @id) + ', name: ' + @name + ' ] 的信息成功!';
    go
    --test
    select * from student order by id;
    select * from classes;
    delete classes where id = 7;

    显示自定义消息raiserror

    if (object_id('tgr_message', 'tr') is not null)
        drop trigger tgr_message
    go
    create trigger tgr_message
    on student
        after insert, update
    as raiserror('tgr_message触发器被触发', 16, 10);
    go
    --test
    insert into student values('lily', 22, 1, 7);
    update student set sex = 0 where name = 'lucy';
    select * from student order by id;

    修改触发器

    alter trigger tgr_message
    on student
    after delete
    as raiserror('tgr_message触发器被触发', 16, 10);
    go
    --test
    delete from student where name = 'lucy';

    启用、禁用触发器

    --禁用触发器
    disable trigger tgr_message on student;
    --启用触发器
    enable trigger tgr_message on student;

    查询创建的触发器信息

    --查询已存在的触发器
    select * from sys.triggers;
    select * from sys.objects where type = 'tr';
    --查看触发器触发事件
    select te.* from sys.trigger_events te join sys.triggers t
    on t.object_id = te.object_id
    where t.parent_class = 0 and t.name = 'tgr_valid_data';
    --查看创建触发器语句
    exec sp_helptext 'tgr_message';

    示例,验证插入数据

    if ((object_id('tgr_valid_data', 'tr') is not null))
        drop trigger tgr_valid_data
    go
    create trigger tgr_valid_data
    on student
    after insert
    as
        declare @age int,
                @name varchar(20);
        select @name = s.name, @age = s.age from inserted s;
        if (@age < 18)
        begin
            raiserror('插入新数据的age有问题', 16, 1);
            rollback tran;
        end
    go
    --test
    insert into student values('forest', 2, 0, 7);
    insert into student values('forest', 22, 0, 7);
    select * from student order by id;

    示例,操作日志

    if (object_id('log', 'u') is not null)
        drop table log
    go
    create table log(
        id int identity(1, 1) primary key,
        action varchar(20),
        createdate datetime default getdate()
    )
    go
    if (exists (select * from sys.objects where name = 'tgr_student_log'))
        drop trigger tgr_student_log
    go
    create trigger tgr_student_log
    on student
    after insert, update, delete
    as
        if ((exists (select 1 from inserted)) and (exists (select 1 from deleted)))
        begin
            insert into log(action) values('updated');
        end
        else if (exists (select 1 from inserted) and not exists (select 1 from deleted))
        begin
            insert into log(action) values('inserted');
        end
        else if (not exists (select 1 from inserted) and exists (select 1 from deleted))
        begin
            insert into log(action) values('deleted');
        end
    go
    --test
    insert into student values('king', 22, 1, 7);
    update student set sex = 0 where name = 'king';
    delete student where name = 'king';
    select * from log;
    select * from student order by id;

    总结

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