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Define entity integrity in terms of a relational database.

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  • 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.
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