数据库完整性

 

1)unique key can be null but primariy key cant be null.

2)primariy key can be refrenced to other table as FK.

3)we can have multiple unique key in a table but PK is one and only one.

4)PK in itself is unique key.

nice answer!

1、实体完整性

2、参照完整性

3、用户定义完整性