Database and SQL Concepts Quiz

What is the primary purpose of a database?

• To store data in a structured format

• To allow complex data operations and transactions

• To organize data for easy retrieval

• All of the above

Answer explanation

The primary purpose of a database is to store data in a structured format, allow complex data operations and transactions, and organize data for easy retrieval. Therefore, the correct answer is 'All of the above'.

What does the term 'relation' refer to in a relational database model?

• A table

• A relationship between tables

• A row of data

• A column of data

Answer explanation

In a relational database model, the term 'relation' specifically refers to a table. Each table consists of rows and columns, where rows represent records and columns represent attributes of the data.

Which of the following is a valid relational database key?

• Tuple

• Attribute

• Primary key

• Cardinality

Answer explanation

A primary key is a valid relational database key that uniquely identifies each record in a table. Tuple, attribute, and cardinality are not keys; they refer to different concepts in database terminology.

What is the meaning of 'degree' in a relational database?

• The number of rows in a table

• The number of attributes in a relation

• The number of tables in a database

• The number of keys in a relation

Answer explanation

In a relational database, 'degree' refers to the number of attributes (columns) in a relation (table). Therefore, the correct answer is 'The number of attributes in a relation', as it defines the structure of the table.

Which key uniquely identifies each tuple in a relational database table?

• Foreign key

• Candidate key

• Primary key

• Alternate key

Answer explanation

The primary key uniquely identifies each tuple in a relational database table, ensuring that no two rows have the same key value. Other keys, like foreign keys and candidate keys, serve different purposes in database relationships.

What is the primary difference between a primary key and a candidate key?

• A primary key can have multiple values, but a candidate key cannot

• A candidate key can be chosen as a primary key, but a primary key cannot be a candidate key

• A candidate key uniquely identifies records, but the primary key does not

• A primary key is a combination of multiple candidate keys

Answer explanation

A candidate key is a potential primary key that can uniquely identify records in a table. The primary key is the chosen candidate key, while a primary key cannot serve as a candidate key itself, as it is already designated.

In a relational database, the cardinality of a relation refers to:

• The number of tuples in a relation

• The number of attributes in a relation

• The number of foreign keys

• The number of columns in a table

Answer explanation

In a relational database, cardinality refers to the number of tuples (rows) in a relation (table). Therefore, the correct answer is 'The number of tuples in a relation', as it directly defines the size of the dataset.

What is the domain of an attribute in a relational database model?

• The range of values an attribute can take

• The name of the attribute

• The number of unique values an attribute can hold

• The unique identifier for an attribute

Answer explanation

The domain of an attribute in a relational database model refers to the range of values that the attribute can take. This defines the permissible values for that attribute, making "The range of values an attribute can take" the correct choice.

Which of the following is an example of a foreign key?

• A key in the 'Orders' table that refers to the 'Customer' table

• A key that uniquely identifies a row in the 'Customers' table

• A primary key in the 'Orders' table

• A key used for internal table indexing

Answer explanation

A foreign key is a field in one table that uniquely identifies a row in another table. The correct choice, 'A key in the Orders table that refers to the Customer table', illustrates this relationship.

Which statement correctly describes a 'candidate key'?

• It is any column that can uniquely identify rows in a table

• It is a column that uniquely identifies rows, but it is not the primary key

• It is the key used for referencing another table

• It is the primary key

Answer explanation

A candidate key is a column that can uniquely identify rows in a table, but it is not necessarily the primary key. The correct choice highlights that it can exist alongside a primary key, distinguishing it from other options.