Databases - 1.2 Primary Key

What is a primary key?

• A unique identifier for each record in a table that cannot contain NULL values.

• A duplicate identifier for records in a table.

• A foreign key in a table.

• A non-unique identifier for records in a table.

Answer explanation

A primary key is essential for uniquely identifying each record in a table, ensuring that no two records can have the same key value. It also cannot contain NULL values, making it a reliable reference point.

What is a composite key?

• A composite key is a primary key made up of two or more columns to uniquely identify a record.

• A composite key is a single column used to uniquely identify a record.

• A composite key is a foreign key used to link two tables.

• A composite key is a unique constraint on a single column.

Answer explanation

A composite key consists of two or more columns that together uniquely identify a record in a database table, making the first answer choice correct.

A primary key column can contain duplicate values because:

• It is allowed by database design.

• It ensures data integrity.

• It uniquely identifies each record.

• It can have null values.

Answer explanation

A primary key must uniquely identify each record in a database. This means it cannot contain duplicate values, as duplicates would violate the uniqueness requirement essential for data integrity.

Activity Question: Given a "Library" table with columns BookID, Title, and AuthorID, which column(s) would be the most appropriate primary key?

• BookID

• Title

• AuthorID

• Title and AuthorID

Answer explanation

The most appropriate primary key is BookID because it uniquely identifies each book in the Library table. Title and AuthorID may not be unique, as multiple books can have the same title or be written by the same author.

Which is the best example of a primary key?

• Driver's License Number

• Home Runs Hit

• Price

• First and Last Name

Answer explanation

A primary key uniquely identifies each record in a database. A Driver's License Number is unique to each individual, making it an ideal primary key. In contrast, Home Runs Hit, Price, and First and Last Name can be duplicated.

Which of the following is a method to enforce data integrity in Access?

• Using primary keys

• Using foreign keys

• Using validation rules

• All of the above

Answer explanation

All of the options—using primary keys, foreign keys, and validation rules—are methods to enforce data integrity in Access. They each play a crucial role in ensuring that data remains accurate and consistent.

In Access, what does the term "referential integrity" refer to?

• Ensuring that all data is encrypted

• Ensuring that relationships between tables remain consistent

• Ensuring that all tables have a primary key

• Ensuring that all queries run efficiently

Answer explanation

Referential integrity ensures that relationships between tables remain consistent, meaning that foreign keys in one table must match primary keys in another, preventing orphaned records and maintaining data accuracy.