• Every table must have a primary key.

  • The primary key must be unique and not null.


How to entity integrity may prevent the insertion of a row of data into a table.



  • No two rows of data can be identical.



  • An attempt to insert a row of data that already exists in the table will be prevented.


How to entity integrity is implemented in a relational database.



  • A primary key should be declared in the CREATE TABLE statement



  • The primary key should be UNIQUE and NOT NULL


 

Define referential integrity in terms of a relational database.



  • Relates to the foreign key which must exist in one of two states.



  • Foreign key must exist as a primary key in another table



  • Or, in certain circumstances, be null


 

How to referential integrity may prevent the insertion of a row of data into a table.



  • If foreign key is entered that does not exist as a primary key in the defined table.



  • Or null entry for foreign key when it is defined as not null.


 

How to referential integrity is implemented in a relational DBMS.



  • The foreign key(s) should be declared in the CREATE TABLE statement.



  • The foreign key(s) specification identifies the associated table and should be mandatory (NOT NULL)



  • The foreign key(s) specification identifies the propagation constraints (ON DELETE SET NULL, ON UPDATE CASCADE)


 

How the following propagation constraints can be used to maintain referential integrity:


 

Restricted delete



  • Target rows cannot be deleted until all module rows for that foreign key have been deleted from the related table.


Cascades delete



  • If a target row is deleted, all related rows in the related table are deleted.


Nullifies delete



  • If a target row is deleted, all associated foreign key values in the related table are set to null.