Understanding Database Keys

What is a primary key in a database?

• A primary key can be duplicated across records.

• A primary key is a type of foreign key.

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

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

How does a foreign key differ from a primary key?

• A primary key uniquely identifies records, while a foreign key links records between tables.

• A primary key is used for indexing, while a foreign key is only for data retrieval.

• A primary key can be null, while a foreign key must always be unique.

• A primary key can link records between tables, while a foreign key uniquely identifies records.

What is a composite key and when is it used?

• A composite key is a unique identifier that is not related to any columns in a table.

• A composite key is used to store duplicate records in a table.

• A composite key is used to uniquely identify records in a table when a single column is insufficient.

• A composite key is a type of primary key that can only consist of one column.

Explain the purpose of unique constraints in a database.

• The purpose of unique constraints in a database is to prevent duplicate values in specified columns, ensuring data integrity.

• To enhance the performance of database queries without affecting data integrity.

• To automatically delete duplicate records from the database.

• To allow multiple entries in the same column for flexibility.

What does referential integrity ensure in a database?

• Referential integrity ensures that all tables have the same number of columns.

• Referential integrity ensures that foreign keys correctly reference primary keys in related tables.

• Referential integrity allows any foreign key to reference any table.

• Referential integrity prevents data from being deleted in the database.

How do primary keys and foreign keys relate to each other?

• Primary keys can reference multiple foreign keys in different tables.

• Foreign keys can only exist in the same table as their primary keys.

• Primary keys are used to delete records, while foreign keys are used to create indexes.

• Primary keys uniquely identify records, and foreign keys reference these primary keys to create relationships between tables.

Can a table have multiple primary keys? Why or why not?

• A table can have multiple primary keys as long as they are unique.

• Yes, a table can have multiple primary keys if they are in different columns.

• A table can have multiple primary keys if they are defined in different databases.

• No, a table cannot have multiple primary keys.

What happens if a foreign key does not match any primary key?

• The operation is rejected due to referential integrity violation.

• The operation is completed without any issues.

• The foreign key is ignored during the operation.

• The foreign key is automatically updated.

Why is it important to have unique constraints on certain fields?

• Unique constraints prevent duplicate values in specific fields, ensuring data integrity and accuracy.

• Unique constraints allow for faster data retrieval.

• Unique constraints are only necessary for primary keys.

• Unique constraints can be ignored for large datasets.

How can composite keys improve data organization in a database?

• Composite keys simplify data retrieval by merging tables.

• Composite keys increase data duplication in records.

• Composite keys eliminate the need for primary keys altogether.

• Composite keys improve data organization by ensuring unique identification of records, reducing redundancy, and enhancing data integrity.