觸發器是一種特殊類型的存儲過程，它不同於之前的我們介紹的存儲過程。觸發器主要是通過事件進行觸發被自動調用執行的。而存儲過程可以通過存儲過程的名稱被調用。
Ø 什麼是觸發器
觸發器對表進行插入、更新、刪除的時候會自動執行的特殊存儲過程。觸發器一般用在check約束更加復雜的約束上面。觸發器和普通的存儲過程的區別是：觸發器是當對某一個表進行操作。諸如：update、insert、delete這些操作的時候，系統會自動調用執行該表上對應的觸發器。SQL Server 2005中觸發器可以分為兩類：DML觸發器和DDL觸發器，其中DDL觸發器它們會影響多種數據定義語言語句而激發，這些語句有create、alter、drop語句。
DML觸發器分為：
1、 after觸發器（之後觸發）
a、 insert觸發器
b、 update觸發器
c、 delete觸發器
2、 instead of 觸發器 （之前觸發）
其中after觸發器要求只有執行某一操作insert、update、delete之後觸發器才被觸發，且只能定義在表上。而instead of觸發器表示並不執行其定義的操作（insert、update、delete）而僅是執行觸發器本身。既可以在表上定義instead of觸發器，也可以在視圖上定義。
觸發器有兩個特殊的表：插入表（instered表）和刪除表（deleted表）。這兩張是邏輯表也是虛表。有系統在內存中創建者兩張表，不會存儲在數據庫中。而且兩張表的都是只讀的，只能讀取數據而不能修改數據。這兩張表的結果總是與被改觸發器應用的表的結構相同。當觸發器完成工作後，這兩張表就會被刪除。Inserted表的數據是插入或是修改後的數據，而deleted表的數據是更新前的或是刪除的數據。
Update數據的時候就是先刪除表記錄，然後增加一條記錄。這樣在inserted和deleted表就都有update後的數據記錄了。注意的是：觸發器本身就是一個事務，所以在觸發器裡面可以對修改數據進行一些特殊的檢查。如果不滿足可以利用事務回滾，撤銷操作。
Ø 創建觸發器
語法
create trigger tgr_name
on table_name
with encrypion –加密觸發器
for update...
as
Transact-SQL
# 創建insert類型觸發器
--創建insert插入類型觸發器
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 --插入觸發
as
--定義變量
declare @id int, @name varchar(20), @temp int;
--在inserted表中查詢已經插入記錄信息
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 '添加學生成功！';
go
--插入數據
insert into classes values('5班', getDate());
--查詢數據
select * from classes;
select * from student order by id;
insert觸發器，會在inserted表中添加一條剛插入的記錄。
# 創建delete類型觸發器
--delete刪除類型觸發器
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 --刪除觸發
as
print '備份數據中……';
if (object_id('classesBackup', 'U') is not null)
--存在classesBackup，直接插入數據
insert into classesBackup select name, createDate from deleted;
else
--不存在classesBackup創建再插入
select * into classesBackup from deleted;
print '備份數據成功！';
go
--
--不顯示影響行數
--set nocount on;
delete classes where name = '5班';
--查詢數據
select * from classes;
select * from classesBackup;
delete觸發器會在刪除數據的時候，將剛才刪除的數據保存在deleted表中。
# 創建update類型觸發器
--update更新類型觸發器
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);
--更新前的數據
select @oldName = name from deleted;
if (exists (select * from student where name like '%'+ @oldName + '%'))
begin
--更新後的數據
select @newName = name from inserted;
update student set name = replace(name, @oldName, @newName) where name like '%'+ @oldName + '%';
print '級聯修改數據成功！';
end
else
print '無需修改student表！';
go
--查詢數據
select * from student order by id;
select * from classes;
update classes set name = '五班' where name = '5班';
update觸發器會在更新數據後，將更新前的數據保存在deleted表中，更新後的數據保存在inserted表中。
# update更新列級觸發器
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
--列級觸發器：是否更新了班級創建時間
if (update(createDate))
begin
raisError('系統提示：班級創建時間不能修改！', 16, 11);
rollback tran;
end
go
--測試
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;
更新列級觸發器可以用update是否判斷更新列記錄；
# instead of類型觸發器
instead of觸發器表示並不執行其定義的操作（insert、update、delete）而僅是執行觸發器本身的內容。
創建語法
create trigger tgr_name
on table_name
with encryption
instead of update...
as
T-SQL
# 創建instead of觸發器
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);
--查詢被刪除的信息，病賦值
select @id = id, @name = name from deleted;
print 'id: ' + convert(varchar, @id) + ', name: ' + @name;
--先刪除student的信息
delete student where cid = @id;
--再刪除classes的信息
delete classes where id = @id;
print '刪除[ 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;
# 顯示自定義消息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觸發器被觸發', 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;
# 修改觸發器
alter trigger tgr_message
on student
after delete
as raisError('tgr_message觸發器被觸發', 16, 10);
go
--test
delete from student where name = 'lucy';
# 啟用、禁用觸發器
--禁用觸發器
disable trigger tgr_message on student;
--啟用觸發器
enable trigger tgr_message on student;
# 查詢創建的觸發器信息
--查詢已存在的觸發器
select * from sys.triggers;
select * from sys.objects where type = 'TR';
--查看觸發器觸發事件
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';
--查看創建觸發器語句
exec sp_helptext 'tgr_message';
# 示例，驗證插入數據
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('插入新數據的age有問題', 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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