Understanding DBMS Keys and Constraints

What is a primary key in a database?

• A primary key is a unique identifier for a record in a database.

• A primary key is used to store large text data.

• A primary key can be duplicated across records.

• A primary key is a type of foreign key.

Define a foreign key and its purpose.

• A foreign key is a type of index that speeds up queries.

• A foreign key is used to delete records from a table.

• A foreign key is a unique identifier for a single table.

• A foreign key is a field that links two tables by referencing the primary key of another table, ensuring data integrity.

What are the characteristics of a candidate key?

• A candidate key can be duplicated across rows.

• A candidate key must be unique, irreducible, and non-nullable.

• A candidate key must be a composite key.

• A candidate key can contain null values.

Explain the concept of a composite key.

• A composite key is a single column that uniquely identifies a record.

• A composite key is a unique identifier made up of multiple columns in a database.

• A composite key is used to store images in a database.

• A composite key is a type of foreign key that links to another table.

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

• A primary key can be null and does not enforce uniqueness.

• A primary key cannot be null and uniquely identifies records, while a unique key can be null and also enforces uniqueness.

• A primary key can have duplicate values but must be unique across tables.

• A unique key can only be used in one table and cannot be referenced by foreign keys.

What are domain constraints in a database?

• Domain constraints define the relationships between tables.

• Domain constraints are used to enforce referential integrity.

• Domain constraints determine the structure of the database schema.

• Domain constraints specify the valid values for attributes in a database.

How do referential integrity constraints work?

• Referential integrity constraints maintain consistency between related tables by enforcing rules on foreign key relationships.

• They only apply to primary keys in a single table.

• They allow any data to be entered without restrictions.

• They are used to optimize database performance.

What happens if a foreign key constraint is violated?

• The operation is rejected, maintaining referential integrity.

• The operation is completed successfully, ignoring the constraint.

• The database automatically deletes the related records.

• A warning is issued, but the operation proceeds anyway.

Can a primary key be null? Why or why not?

• Yes, a primary key can be null.

• A primary key can be null if it is part of a composite key.

• A primary key can be null if it is defined as optional.

• No, a primary key cannot be null.

What is the role of a surrogate key in a database?

• The role of a surrogate key in a database is to provide a unique identifier for records that is independent of the actual data.

• A surrogate key is used to store large amounts of data.

• A surrogate key is a foreign key that links tables together.

• A surrogate key is a type of index that speeds up queries.