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，級別 16，狀態 0，第 1 行--UPDATE 語句與 CHECK 約束"CK_Blance"沖突。該沖突發生于數據庫"mydb"，表"dbo.account", column 'balance'。--語句已終止。go--alter table account--alter COlumn balance intgoalter table accountadd constraint CK_Blance check(balance >= 0)goalter table accountdrop constraint CK_Blance--定一個事務--從liyong扣錢往mali加錢begin transactionupdate account set balance = balance - 1000 where id = '620101'if((select balance output from account where id = '620101') < 0)beginPRINT('余額不足！');ROLLBACK;endelsebegin  update account set balance = balance + 1000 where id = '620106'  commit;  PRINT('轉賬成功！');endgosp_help--備份設備sp_addumpdevice 'disk', 'xk_bak' ,'d:/xk_bak'--備份數據庫backup database mydbto xk_bak--還原數據庫restore database mydb from disk = 'd:/xk_bak'with replace; --覆蓋