What is a primary key and why is it important?
Theme: Database Design Role: Database Administrator Function: Technology
Interview Question for Database Administrator: See sample answers, motivations & red flags for this common interview question. About Database Administrator: Manages and optimizes databases for efficient data storage and retrieval. This role falls within the Technology function of a firm. See other interview questions & further information for this role here
Sample Answer
Example response for question delving into Database Design with the key points that need to be covered in an effective response. Customize this to your own experience with concrete examples and evidence
- Definition of a primary key: A primary key is a unique identifier for each record in a database table. It is a column or a set of columns that uniquely identifies each row in the table
- Importance of a primary key: 1. Uniqueness: A primary key ensures that each record in a table is uniquely identified, preventing duplicate or redundant data. 2. Data integrity: It enforces data integrity by ensuring that each record has a unique identifier, preventing data inconsistencies. 3. Referential integrity: Primary keys are used as references in relationships between tables, ensuring the integrity of data across multiple tables. 4. Indexing: Primary keys are automatically indexed, which improves the performance of data retrieval operations
- Choosing a primary key: 1. Uniqueness: A primary key should be unique and not repeated in any other record. 2. Simplicity: It should be simple and easy to understand. 3. Stability: A primary key should be stable and not change frequently. 4. Non-nullability: It should not contain null values. 5. Scalability: It should be scalable to accommodate future growth of the database
- Types of primary keys: 1. Natural keys: These are primary keys that are derived from the data itself, such as a social security number or an employee ID. 2. Surrogate keys: These are artificially created primary keys, often using an auto-incrementing number or a GUID. 3. Composite keys: These are primary keys that consist of multiple columns, used when a single column cannot uniquely identify a record
- Examples of primary keys: 1. In a customer table, the primary key could be a unique customer ID. 2. In an employee table, the primary key could be an employee ID. 3. In a product table, the primary key could be a product code
Underlying Motivations
What the Interviewer is trying to find out about you and your experiences through this question
- Knowledge & understanding of database design: Assessing if the candidate understands the concept and importance of primary keys in database design
- Problem-solving skills: Evaluating the candidate's ability to identify and implement primary keys to ensure data integrity and efficient data retrieval
- Attention to detail: Determining if the candidate recognizes the significance of selecting unique and non-null primary keys for accurate data management
Potential Minefields
How to avoid some common minefields when answering this question in order to not raise any red flags
- Lack of understanding: Not being able to explain what a primary key is or its purpose
- Confusion with other keys: Mixing up primary keys with foreign keys or unique keys
- Inability to provide examples: Not being able to give real-world examples of primary keys
- Ignoring importance: Downplaying the significance of primary keys in database design and data integrity
- Lack of knowledge on indexing: Not understanding how primary keys are used for indexing and improving query performance