废话不多说，直接上代码
create database mydb use mydb go create table account( id varchar(16), name varchar(16), balance float ) go select * from account insert 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" 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