Database Management: Super Keys and Data Integrity

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Questions and Answers

What is the main purpose of a super key in a database?

To locate specific tuples using their unique properties. (correct)
To manage user permissions effectively.
To prevent all duplicate records.
To serve as a primary key only.

Which statement regarding primary keys is correct?

Primary keys can be repeated across different tables.
A table can have multiple primary keys.
Only one primary key can be defined in a table. (correct)
NULL values are permitted in primary key columns.

What is a distinguishing feature of unique keys compared to primary keys?

They can have NULL values. (correct)
Only one unique key can exist in a table.
They have a strict requirement for data consistency.
They ensure referential integrity between tables.

Which characteristic is true of super keys?

They can serve as foreign keys for relational integrity. (B) Signup and view all the answers

Which of the following statements about primary keys is NOT true?

Primary keys can include duplicate values. (D) Signup and view all the answers

How are super keys beneficial for database performance?

By enabling efficient indexing and faster data access. (B) Signup and view all the answers

What defines a primary key within a relational database?

It can be made up of multiple columns. (C) Signup and view all the answers

What is the correct definition of entity integrity in the context of primary keys?

A state where primary keys are mandatory and cannot be NULL. (B) Signup and view all the answers

What is a primary characteristic of a candidate key in a database management system?

It uniquely identifies a record within a table. (B) Signup and view all the answers

Which statement about super keys is true?

A super key can be composed of any number of attributes. (C) Signup and view all the answers

Which of the following best defines a referential integrity constraint?

It restricts a product to be made by only one company. (A) Signup and view all the answers

What distinguishes a primary key from a candidate key?

A primary key must be chosen from the set of candidate keys. (A) Signup and view all the answers

What type of constraint requires the uniqueness of value combinations in a database?

Super key constraint. (B) Signup and view all the answers

Which of the following is false regarding keys in relational databases?

A foreign key is required to be unique within its table. (B) Signup and view all the answers

What is the purpose of having constraints in SQL?

To ensure data accuracy and integrity. (C) Signup and view all the answers

Which of the following is NOT an example of a type of key in a relational model?

Secondary key (C) Signup and view all the answers

What is the maximum number of NULL values that can be stored in a column with a unique constraint?

One (A) Signup and view all the answers

Which of the following best describes a foreign key?

A combination of columns that establishes a relationship between two tables (B) Signup and view all the answers

In the context of SQL constraints, which statement is true about candidate keys?

They are a subset of super keys. (B) Signup and view all the answers

Which of the following statements is incorrect regarding unique keys?

A unique key can store multiple NULL values. (A) Signup and view all the answers

What is an example of a primary key?

A column that uniquely identifies each record in a table (A) Signup and view all the answers

In SQL, what does a super key refer to?

Any combination of columns that can uniquely identify a row. (C) Signup and view all the answers

How does the foreign key maintain a table's uniqueness?

By enforcing referential integrity between two tables (D) Signup and view all the answers

Which of the following is NOT a distinctive characteristic of a unique key?

Must contain only one column (C) Signup and view all the answers

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Study Notes

Super Key

Super keys uniquely identify tuples in a table by combining one or more attributes.
They prevent duplicate entries and ensure data consistency within a dataset.
Super keys can function as foreign keys, establishing reliable links between related tables.
They improve database performance by facilitating efficient indexing and quicker data access.

Primary Key

A primary key is a single column used to identify each row uniquely in a table.
It enforces entity integrity and cannot contain duplicate or NULL values.
A table can only have one primary key, which is critical to maintaining data accuracy.
Choosing a primary key should be done carefully as it is typically infrequently changed.

Unique Key

A unique key constraint identifies tuples independently, allowing multiple unique keys per table.
It supports unique identification with the ability to allow one NULL value per column.
Unique keys can also act as foreign keys, ensuring integrity and uniqueness in databasing.

Candidate Key

Candidate keys serve as potential primary keys and must be unique and minimally redundant within a table.
These keys allow for the identification of single records without any ambiguity.

Foreign Key Constraint

A foreign key is a column or set of columns that create a link between data in two tables.
It helps maintain referential integrity by controlling what data can be stored in related tables.
Example: In a "Purchase" table, a column (prodName) can reference the name column in a "Product" table, ensuring that only valid product names are recorded.

Constraints Overview

Constraints are essential to maintain data integrity within a database.
Key constraints, including primary and unique keys, prevent unwanted duplicates and null entries.
Participation constraints define whether all tuples in one table must have corresponding entries in another table.

Entity-Relationship (ER) Modeling

ER modeling simplifies database design by focusing on three main concepts:
- Generalization: Abstraction of shared characteristics of entities.
- Specialization: Creating sub-entities based on specific attributes of a general entity.