insert into account(id,name,balance) values('620101','liyong',300)
insert into account(id,balance) values('620106','mali',400)
--insert into account(id,balance) values('620009','chenying',800)
insert into account(id,balance) values('646009',800)
--delete from account where id = '620009'
go
update account set balance = balance - 1000 where id = '620101'
update account set balance = balance + 1000 where id = '620106'
--消息 547，级别 16，状态 0，第 1 行
--UPDATE 语句与 CHECK 约束"CK_Blance"冲突。该冲突发生于数据库"mydb"，表"dbo.account",column 'balance'。
--语句已终止。

go
--alter table account
--alter COlumn balance int
go
alter table account
add constraint CK_Blance check(balance >= 0)
go
alter table account
drop constraint CK_Blance
--定一个事务
--从liyong扣钱往mali加钱
begin transaction
update account set balance = balance - 1000 where id = '620101'
if((select balance output from account where id = '620101') < 0)
begin
PRINT('余额不足！');
ROLLBACK;
end
else
begin
update account set balance = balance + 1000 where id = '620106'
commit;
PRINT('转账成功！');
end
go
sp_help
--备份设备
sp_addumpdevice 'disk','xk_bak','d:\xk_bak'
--备份数据库
backup database mydb
to xk_bak
--还原数据库
restore database mydb from disk = 'd:\xk_bak'
with replace; --覆盖