SQL Server 触发器

2016/01/07 15:57
阅读数 18

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。

Ø 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。

对表的操作

Inserted逻辑表

Deleted逻辑表

增加记录(insert)

存放增加的记录

删除记录(delete)

存放被删除的记录

修改记录(update)

存放更新后的记录

存放更新前的记录

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。

Ø 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;
展开阅读全文
打赏
0
0 收藏
分享
加载中
更多评论
打赏
0 评论
0 收藏
0
分享
在线直播报名
返回顶部
顶部