Relational Model

Choose the option that correctly answer the question.

$(5$ Points$)$

Which of the following sentences is TRUE?

$(2$ Pnts$)$

a$.$ The proper use of foreign keys is crucial to exercising data redundancy control.

b$.$ The referential integrity rule requires that every null foreign key value must reference an existing primary key value.

c$.$ A table can be logically connected to another table by defining a primary key.

d$.$ It is possible to delete a row in one table whose primary key does not have a matching foreign key value in another table.

Which of the following is true about a foreign key?

a$.$ It could be not$-$unique and nullable $($has nulls$).$

b$.$ It can relate to multiple rows in another table.

c$.$ It can relate to columns which are not primary keys.

d$.$ It must be defined in all tables in the database.

A primary key in a table

a$.$ must be different from a primary key in another table

b$.$ must be different from foreign keys in another tables

c$.$ can be the same value as other primary key values in the same table

d$.$ must not contain NULL

Referential integrity is where

a$.$ references in the database are identical to references in an ER diagram.

b$.$ foreign key always refers to a primary key value or is NULL.

c$.$ primary keys in one table always refer to primary keys in another table.

d$.$ foreign keys in one table always refer to foreign keys in another table.