Data Modeling вопросы и ответы для интервью
Вопрос 11. What is the difference between a primary key and a unique key?
Both primary keys and unique keys enforce uniqueness in a column, but a table can have only one primary key, whereas it can have multiple unique keys.
Example:
Example: In a 'Person' table, the 'SSN' column can be a primary key, ensuring each person has a unique social security number.
Вопрос 12. Explain the ACID properties in the context of database transactions.
ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are reliable, consistent, and maintain data integrity.
Example:
Example: If a transaction fails at any point, the entire transaction is rolled back, ensuring atomicity.
Вопрос 13. What is a data warehouse, and how does it differ from a database?
A data warehouse is a large, centralized repository of data that is optimized for analysis and reporting. It differs from a database in its focus on historical and aggregated data for decision support.
Example:
Example: Storing years of sales data in a data warehouse for trend analysis.
Вопрос 14. How do you handle concurrency issues in a database?
Concurrency control mechanisms, such as locking or optimistic concurrency control, are used to manage simultaneous access to data and prevent conflicts during transactions.
Example:
Example: Using row-level locking to ensure that two transactions don't modify the same row simultaneously.
Вопрос 15. What is a star schema in data warehousing?
A star schema is a type of data warehouse schema where a central fact table is connected to dimension tables through foreign key relationships. It simplifies queries for analytical purposes.
Example:
Example: In a retail data warehouse, a 'Sales' fact table is connected to 'Product,' 'Time,' and 'Location' dimension tables.
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