黑马视频-事务

--A账户向B账户转账 
alter table bank add constraint check (balance>=10) --添加约束
insert into bank(‘001‘,1000)
insert into bank(‘002‘,10)
//============================================================================
update bank set balance=balance-1000 where cid=‘001‘
update bank set balance=balance+1000 where cid=‘002‘
//由于存在大于等于10的约束，第一句执行失败，数据没有发生变化，第二句执行成功（1010）//
--1.打开事物
begin tran
declare @sum int=0
 update bank set balance=balance-1000 where cid=‘001‘
 set @sum=@sum+@@error
 update bank set balance=balance+1000 where cid=‘002‘
 set @sum=@sum+@@error
 if @sum<>0
  begin 
   rollback
   print ‘回滚‘
  end
 else 
  begin
    commit tran
    print ‘提交‘
  end