create database mydbuse mydbgocreate table account( id varchar(16), name varchar(16), balance float)goselect * from accountinsert into account(id, name, balance) values('620101', 'liyong', 300)insert into account(id, name, balance) values('620106', 'mali', 400)--insert into account(id, name, balance) values('620009', 'chenying', 800)insert into account(id, name, balance) values('646009', 'chenying', 800)--delete from account where id = '620009'goupdate 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 intgoalter table accountadd constraint CK_Blance check(balance >= 0)goalter table accountdrop constraint CK_Blance--定一个事务--从liyong扣钱往mali加钱begin transactionupdate account set balance = balance - 1000 where id = '620101'if((select balance output from account where id = '620101') < 0)beginPRINT('余额不足！');
ROLLBACK;
endelsebegin update account set balance = balance + 1000 where id = '620106' commit;
PRINT('转账成功！');
endgosp_help--备份设备sp_addumpdevice 'disk', 'xk_bak' ,'d:xk_bak'--备份数据库backup database mydbto xk_bak--还原数据库restore database mydb from disk = 'd:xk_bak'with replace;
--覆盖