Candidate key

Definition

A candidate key is a minimal set of attributes that uniquely identifies a record in a relational database table. Each candidate key can be used to uniquely retrieve data, ensuring that no two rows have the same value for this key, while also being the smallest possible set of attributes needed for that uniqueness. Understanding candidate keys is crucial as they directly relate to functional dependencies, normalization processes, and the establishment of relationships between tables.

5 Must Know Facts For Your Next Test

1. A candidate key must be unique across all records in the table and cannot contain any redundant attributes.
2. There can be multiple candidate keys in a table, but only one can be chosen as the primary key.
3. Candidate keys help in the normalization process by establishing clear functional dependencies between attributes.
4. Identifying candidate keys is essential for ensuring data integrity and preventing duplicate entries in database tables.
5. Candidate keys are critical for defining relationships between different tables, especially when establishing foreign keys.

Review Questions

• How do candidate keys relate to functional dependencies in a database?
  • Candidate keys are closely linked to functional dependencies because they determine which attributes can uniquely identify records within a table. When analyzing functional dependencies, it's important to identify candidate keys since they help establish which attributes rely on others for their values. This relationship plays a crucial role in normalization, as understanding these dependencies allows us to minimize redundancy and ensure that each piece of data is stored efficiently.
• What role do candidate keys play in the normalization process when designing a relational database schema?
  • In the normalization process, candidate keys are essential as they help eliminate redundancy and ensure that each piece of data is stored logically. By identifying candidate keys, we can determine how attributes depend on one another and organize the data into appropriate normal forms. This organization helps prevent anomalies during data manipulation, such as insertion or deletion anomalies, thereby promoting data integrity and consistency throughout the database.
• Evaluate the impact of improperly defined candidate keys on the relationships between tables in a relational database.
  • Improperly defined candidate keys can lead to significant issues in a relational database, including data inconsistency and integrity problems. If candidate keys do not uniquely identify records, it may result in duplicate entries or difficulty establishing relationships through foreign keys. This lack of clarity can compromise the overall design of the database, making it challenging to retrieve accurate information and enforce referential integrity. Ultimately, well-defined candidate keys are fundamental to maintaining robust relationships between tables and ensuring the database functions effectively.

Related terms

Primary Key: The primary key is a specific candidate key that has been selected to uniquely identify records in a table, ensuring that each entry is distinct and non-null.

Functional Dependency: A functional dependency is a relationship between two attributes, typically between a primary key and another attribute, where the value of one attribute depends on the value of another.

Super Key: A super key is any combination of columns in a table that can uniquely identify a row, but it may contain unnecessary attributes beyond those needed for uniqueness.