Data Modeling вопросы и ответы для интервью
Вопрос 21. What is a surrogate vs. natural key. When would you use one over the other?
A surrogate key is an artificial identifier, while a natural key is based on existing data attributes. Surrogate keys are often preferred for simplicity, consistency, and to avoid changes in natural keys.
Example:
Example: Using an auto-incremented 'ID' as a surrogate key for a 'Customer' table, even if the 'SSN' could be a natural key.
Вопрос 22. What is a data mart, and how does it differ from a data warehouse?
A data mart is a subset of a data warehouse that is focused on specific business functions or user groups. It is smaller in scope compared to a data warehouse, which covers the entire organization.
Example:
Example: Creating a data mart specifically for finance-related data within a larger enterprise data warehouse.
Вопрос 23. What are some common data modeling tools, and why are they essential?
Common data modeling tools include ERwin, ER/Studio, and PowerDesigner. These tools assist in designing, visualizing, and documenting database structures, ensuring efficient communication and collaboration.
Example:
Example: Using ERwin to create an ERD for a new database schema.
Вопрос 24. What is a composite key, and when would you use it?
A composite key is a key that consists of multiple columns to uniquely identify a record. It is used when a single column cannot guarantee uniqueness, but the combination of multiple columns does.
Example:
Example: Using a composite key of ('DepartmentID', 'EmployeeID') to uniquely identify employees within each department.
Вопрос 25. Explain the concept of a self-referencing table.
A self-referencing table is a table that includes a foreign key that references its own primary key. It is used to represent hierarchical relationships within the same entity.
Example:
Example: Creating an 'Employee' table with a 'ManagerID' foreign key referencing the same 'EmployeeID' column to represent the employee-manager relationship.
Самое полезное по оценкам пользователей: