SQL Server触发器详解-PHP开发-php.cn

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

无

删除记录（delete）

无

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

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# 创建insert类型触发器

--创建insert插入类型触发器
if (object_id(&#39;tgr_classes_insert&#39;, &#39;tr&#39;) 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 &#39;添加学生成功！&#39;;
go
--插入数据
insert into classes values(&#39;5班&#39;, getDate());
--查询数据
select * from classes;
select * from student order by id;

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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(&#39;tgr_classes_delete&#39;, &#39;TR&#39;) is not null)
    drop trigger tgr_classes_delete
go
create trigger tgr_classes_delete
on classes
    for delete --删除触发
as
    print &#39;备份数据中……&#39;;   
    if (object_id(&#39;classesBackup&#39;, &#39;U&#39;) 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 &#39;备份数据成功！&#39;;
go
--
--不显示影响行数
--set nocount on;
delete classes where name = &#39;5班&#39;;
--查询数据
select * from classes;
select * from classesBackup;

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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(&#39;tgr_classes_update&#39;, &#39;TR&#39;) 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 &#39;%&#39;+ @oldName + &#39;%&#39;))
        begin
            --更新后的数据
            select @newName = name from inserted;
            update student set name = replace(name, @oldName, @newName) where name like &#39;%&#39;+ @oldName + &#39;%&#39;;
            print &#39;级联修改数据成功！&#39;;
        end
    else
        print &#39;无需修改student表！&#39;;
go
--查询数据
select * from student order by id;
select * from classes;
update classes set name = &#39;五班&#39; where name = &#39;5班&#39;;

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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(&#39;tgr_classes_update_column&#39;, &#39;TR&#39;) 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(&#39;系统提示：班级创建时间不能修改！&#39;, 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 = &#39;四班&#39; where id = 7;

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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

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# 创建instead of触发器

if (object_id(&#39;tgr_classes_inteadOf&#39;, &#39;TR&#39;) 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 &#39;id: &#39; + convert(varchar, @id) + &#39;, name: &#39; + @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 &#39;删除[ id: &#39; + convert(varchar, @id) + &#39;, name: &#39; + @name + &#39; ] 的信息成功！&#39;;
go
--test
select * from student order by id;
select * from classes;
delete classes where id = 7;

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# 显示自定义消息raiserror

if (object_id(&#39;tgr_message&#39;, &#39;TR&#39;) is not null)
    drop trigger tgr_message
go
create trigger tgr_message
on student
    after insert, update
as raisError(&#39;tgr_message触发器被触发&#39;, 16, 10);
go
--test
insert into student values(&#39;lily&#39;, 22, 1, 7);
update student set sex = 0 where name = &#39;lucy&#39;;
select * from student order by id;

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# 修改触发器

alter trigger tgr_message
on student
after delete
as raisError(&#39;tgr_message触发器被触发&#39;, 16, 10);
go
--test
delete from student where name = &#39;lucy&#39;;

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# 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;

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# 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 = &#39;TR&#39;;
 
--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 = &#39;tgr_valid_data&#39;;
 
--查看创建触发器语句
exec sp_helptext &#39;tgr_message&#39;;

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# 示例，验证插入数据

   
if ((object_id(&#39;tgr_valid_data&#39;, &#39;TR&#39;) 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(&#39;插入新数据的age有问题&#39;, 16, 1);
        rollback tran;
    end
go
--test
insert into student values(&#39;forest&#39;, 2, 0, 7);
insert into student values(&#39;forest&#39;, 22, 0, 7);
select * from student order by id;

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# 示例，操作日志

if (object_id(&#39;log&#39;, &#39;U&#39;) 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 = &#39;tgr_student_log&#39;))
    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(&#39;updated&#39;);
    end
    else if (exists (select 1 from inserted) and not exists (select 1 from deleted))
    begin
        insert into log(action) values(&#39;inserted&#39;);
    end
    else if (not exists (select 1 from inserted) and exists (select 1 from deleted))
    begin
        insert into log(action) values(&#39;deleted&#39;);
    end
go
--test
insert into student values(&#39;king&#39;, 22, 1, 7);
update student set sex = 0 where name = &#39;king&#39;;
delete student where name = &#39;king&#39;;
select * from log;
select * from student order by id;

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