Relational Model Constraints Quiz

A primary key is a specific column or a set of columns in a relational database that uniquely identifies each record in a table. This uniqueness ensures that no two rows have the same primary key value, allowing for efficient data retrieval and maintaining data integrity within the database.

The Not Null constraint explicitly prevents a column from having NULL values, ensuring that every record must contain a valid entry. This is crucial for maintaining data integrity, as it guarantees that essential information is always present in the database.

A foreign key establishes a link between two tables in a database by referencing the primary key of another table. This relationship ensures data integrity, allowing the foreign key to maintain consistent and valid references to the corresponding records in the primary table, thereby enforcing relational database principles.

A table can only have one primary key, which uniquely identifies each record within that table. The primary key ensures that no two rows can have the same value for that key, maintaining data integrity. While a table can have multiple unique constraints, only one primary key is allowed.

Referential integrity is a database concept that ensures relationships between tables remain consistent. It mandates that any foreign key value in one table must correspond to a primary key value in another, preventing orphaned records and maintaining the integrity of the data across related tables.

The UNIQUE constraint in a database ensures that all values in a specified column are distinct. This means that no two rows can have the same value in that column, effectively preventing duplicate entries. This feature is crucial for maintaining data integrity and ensuring accurate information retrieval.

A candidate key is a set of attributes that can uniquely identify each row in a database table. Unlike primary keys, which are selected from candidate keys, a candidate key itself does not have to be a primary key. Its uniqueness ensures that no two rows have the same values for those attributes.

A foreign key establishes a link between two tables in a database by referencing the primary key of another table. This relationship ensures data integrity, as the foreign key value must match an existing primary key value, thereby maintaining consistent and valid data across related tables.

A domain constraint in the relational model ensures that the data entered into a column adheres to a specific type or format, such as restricting values to integers, dates, or predefined options. This helps maintain data integrity and consistency within the database by preventing invalid data entries.

A CHECK constraint in a database enforces a logical condition that data must meet before it can be inserted or updated in a table. This ensures data integrity by allowing only valid entries according to the specified criteria, such as ranges or specific values, thereby preventing erroneous data from being stored.

RESTRICT prevents the deletion of a row that is referenced by a foreign key by enforcing referential integrity. If an attempt is made to delete a row that is still linked to another table through a foreign key, the RESTRICT action will block the deletion, ensuring that no orphaned records are created in the database.

An attribute can serve dual roles in a database. As a primary key, it uniquely identifies each record in its own table. Simultaneously, it can act as a foreign key by referencing the primary key of another table, establishing a relationship between the two tables while maintaining data integrity.