23、Constraint and delete

• NOT NULL
• UNIQUE：CONSTRAINT uc_PersonID UNIQUE (Id_P,LastName)
• PRIMARY KEY：CONSTRAINT pk_PersonID PRIMARY KEY (Id_P)
• FOREIGN KEY：FOREIGN KEY (Id_P) REFERENCES Persons(Id_P)
• CHECK：CONSTRAINT chk_Person CHECK (Id_P>0 AND City='Sandnes')
• DEFAULT：City varchar(255) DEFAULT 'Sandnes'

 

ON DELETE CASCADE→关系表的级联删除