摘要: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。本篇JavaEE进阶教程将为大家讲解JavaEE进阶编程的知识点,看完这篇文章会让你对JavaEE进阶编程的知识点有更加清晰的理解和运用。
SQL Server 触发器
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。本篇JavaEE进阶教程将为大家讲解JavaEE进阶编程的知识点,看完这篇文章会让你对JavaEE进阶编程的知识点有更加清晰的理解和运用。
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)
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。由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。
创建触发器
语法
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,并赋值
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;
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