文档介绍：Qingdao TechnologicalUniversityDepartment puter Engineering第五章数据库完整性2Department puter EngineeringQingdao TechnologicalUniversity概述?数据库的完整性?指数据的正确性和相容性?数据的安全性?指保护数据库防止恶意的破坏和非法的存取3Department puter EngineeringQingdao TechnologicalUniversity概述?为维护数据库的完整性,DBMS必须能够?提供定义完整性约束条件的机制?一般由SQL的DDL语句来实现?作为数据库模式的一部分存入数据字典中?提供完整性检查的方法?一般在INSERT、UPDATE、DELETE语句执行完后开始检查?违约处理?当违背完整性约束条件时,采取的动作(拒绝或级连)4Department puter EngineeringQingdao TechnologicalUniversity实体完整性?实体完整性定义?在CREATE TABLE中用PRIMARY KEY定义?单属性?列级约束?表级约束?多属性?表级约束5Department puter EngineeringQingdao TechnologicalUniversity实体完整性?将Student表中的Sno属性定义为码CREATE TABLE Student(Sno CHAR(9) PRIMARY KEY,/*列级*/sName CHAR(20) NOT NULL,Ssex CHAR(2), Sage SMALLINT,Sdept CHAR(20));6Department puter EngineeringQingdao TechnologicalUniversity实体完整性?将Student表中的Sno属性定义为码CREATE TABLE Student(Sno CHAR(9),sName CHAR(20) NOT NULL,Ssex CHAR(2), Sage SMALLINT,Sdept CHAR(20) PRIMARY KEY (Sno)/*表级*/);7Department puter EngineeringQingdao TechnologicalUniversity实体完整性?将SC表中的Sno, Cno属性组定义为码CREATE TABLE SC(Sno CHAR(9) NOT o CHAR(4) NOT NULL, Grade SMALLINT, PRIMARY KEY (Sno, Cno)/*表级*/);8Department puter EngineeringQingdao TechnologicalUniversity实体完整性?实体完整性检查和违约处理?当插入一条记录或修改主码时?检查主码值是否唯一?检查主码的各个属性是否为空9Department puter EngineeringQingdao TechnologicalUniversity参照完整性?参照完整性定义?在CREATE TABLE中用FOREIGN KEY短语定义哪些列为外码,用REFERENCES短语指明这些外码参照哪些表的主码10Department puter EngineeringQingdao TechnologicalUniversity参照完整性?定义SC中的参照完整性CREATE TABLE SC(Sno CHAR(9) NOT o CHAR(4) NOT NULL, Grade SMALLINT, PRIMARY KEY (Sno, Cno)/*表级实体完整性*/ FOREIGN KEY(Sno) REFERENCES Student(Sno),FOREIGN o) REFERENCES o),/*标记参照完整性*/);