浅谈 Sql Server 触发器

select * from sys.triggers

--------------- 初始化环境 ---------------

create database TriggerDatabase
use TriggerDatabase
go

if exists(select * from sysobjects where name=‘bank‘)
   drop table bank

create table bank -- 账户信息表
(
   userName      varchar(10) not null,  --顾客名
   cardID        varchar(10) not null,  --卡号
   currentMoney  money       not null   --当前余额
)

if exists(select * from sysobjects where name=‘transInfo‘)
   drop table transInfo

create table transInfo --交易信息表
(
   cardID     varchar(10) not null,  --卡号
   transType  char(4)     not null,  --交易类型(存入/支取)
   transMoney money       not null,  --交易金额
   transDate  datetime    not null   --交易日期
)
go

--------------- 添加约束 ---------------
alter table bank
add constraint CK_currentMoney check(currentMoney>=1);

alter table transInfo
add constraint DF_transDate default(getdate()) for transDate;

alter table transInfo
add constraint CK_transType check(transType in(‘支取‘,‘存入‘));

--------------- 添加测试数据 ---------------
/* 张三 1000元 */
insert into bank(userName,cardID,currentMoney)
        values(‘张三‘,‘1001 0001‘,1000);
/* 李四 1元 */
insert into bank(userName,cardID,currentMoney)
        values(‘李四‘,‘1001 0002‘,1);
/* 张三 支取 200元 */
insert into transInfo(cardID,transType,transMoney)
        values(‘1001 0001‘,‘支取‘,200);

--------------- 查看结果 ---------------
select * from bank;
select * from transInfo;
go

create trigger [ schema_name. ] -- 触发器所属架构
               trigger_name     -- 触发器名称
on { table | view }       -- 触发器的表或视图
   [ with encryption ]    -- 加密dml触发器定义(后面详解)
{ for | after } 
   /* after：只有在触发它的SQL语句执行成功后才能激发。
             (只能对“表”定义after) */
    { insert,update,delete } 
as
    /* SQL语句... */
go

--查看当前数据库中的所有触发器
select * from sys.triggers

------------------ insert 触发器 ------------------
use TriggerDatabase
go
if exists(select * from sysobjects 
           where name=‘trig_insert_transInfo‘)
drop trigger trig_insert_transInfo
go

-- create trigger必须是批处理(go)的第一句

create trigger trig_insert_transInfo
on transInfo for insert
as
    declare @_transType   char(4),  --定义变量
              @_transMoney  money,
            @_cardID      char(10),
            @balance      money     --所剩余额

    -- 从inserted临时表中获取记录值
    select  @_transType = transType,
           @_transMoney = transMoney,
           @_cardID = cardID 
           from inserted

    if(@_transType = ‘支取‘)
       update bank set currentMoney=currentMoney-@_transMoney
              where cardID = @_cardID;
    else 
       update bank set currentMoney=currentMoney+@_transMoney
              where cardID = @_cardID;

    --显示交易金额
    print ‘交易成功！ 交易金额：‘
          + convert(varchar(20),@_transMoney)

    --显示所剩余额
    select @balance = currentMoney from bank 
           where cardId = @_cardID

    print ‘卡号：‘+@_cardID 
          + ‘ 余额：‘+convert(varchar(20),@balance);
go

------------------ 测试触发器 ------------------
-- delete from transInfo
set nocount on --不显示T-SQL影响的记录行数

insert into transInfo(cardID,transType,transMoney)
             values(‘1001 0001‘,‘支取‘,200);
insert into transInfo(cardID,transType,transMoney)
             values(‘1001 0001‘,‘存入‘,10000);
--查看结果
select * from bank
select * from transInfo
复制代码

/* 实现: 当清除‘交易信息表‘的数据时，
         自动备份被清除的数据到backupTable表中
*/

------------------ delete 触发器 ------------------
use TriggerDatabase
go

if exists (select * from sysobjects 
           where name=‘trig_delete_transInfo‘)
drop trigger trig_delete_transInfo
go

create trigger trig_delete_transInfo
on transInfo after delete  --  for | after
as
   print ‘开始备份数据，请稍后......‘
   -- 如果数据库中，不存在 backupTable 表
   if not exists(select * from sysobjects 
                  where name=‘backupTable‘)
      select * into backupTable from deleted --deleted临时表
   else
      insert into backupTable select * from deleted
  
   print ‘备份成功，备份表 backupTable 中的数据为：‘
        select * from backupTable;
go


------------------ 测试触发器 ------------------
set nocount on

delete from transInfo; --测试

--查看结果
select * from transInfo
select * from backupTable

------------------ update 触发器 ------------------
use TriggerDatabase
go

if exists (select * from sysobjects 
           where name=‘trig_update_bank‘)
drop trigger trig_update_bank
go

create trigger trig_update_bank
on bank for update  --在bank表上创建update触发器
as
   declare @beforeMoney money,
           @afterMoney  money,
           @currentTrans money --当前交易金额

   --从deleted临时表，获取交易前的余额
   select @beforeMoney = currentMoney from deleted;
   --从inserted临时表，获取交易后的余额
   select @afterMoney = currentMoney from inserted;
   
   if abs(@afterMoney-@beforeMoney) > 2000
      begin
        print ‘当前交易金额为：‘ +
              convert(varchar(20),abs(@afterMoney-@beforeMoney))
        -- 自定义错误消息
        raiserror(‘每次交易金额不能超过2000元，交易失败！‘,16,1)
       
        rollback transaction --回滚事务，撤销交易！
        /* 注意：
           触发器是一个特殊的事务单元
           不需显示声明begin transaction
        */
      end
go

------------------ 测试触发器 ------------------
set nocount on

--测试1: 在 bank表触发 update触发器
update bank set currentMoney = currentMoney + 25000
       where cardID = ‘1001 0001‘

--测试2: 通过 transInfo表的 trig_insert_transInfo触发器
--             间接触发 bank表的 trig_update_bank触发器

insert into transInfo(cardID,transType,transMoney)
             values(‘1001 0001‘,‘存入‘,10000);

--查看结果
select * from bank
select * from transInfo

create table testTable(a int null, b int null)
  go
  create trigger my_trig
  on testTable for insert
  as
     if update(b)
     print ‘列b已被修改！‘
  go
 
  insert into testTable(b) values(123);

  -- drop table testTable

create table testTable2(a int null, b int null)
  go

  create trigger my_trig2
  on testTable2 for insert
  as
     if ( columns_updated() & 2 = 2 )
     print ‘列b已被修改！‘
  go

  insert into testTable2(b) values(123);
 
  -- drop table testTable2