Data Modeling Basics Interview Questions

All 52 questions

1. Can you explain database normalization and the first three normal forms with examples?

   Asked in 4 of 274 interviews · last asked Sep 8 · Concept · Mid-level

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   Normalization reduces repeated data and prevents update problems. 1NF stores one value per cell, with no repeating groups. 2NF also requires every non-key column to depend on each whole candidate key, not part of one. 3NF also removes dependencies where a non-key column depends on a key through another non-key column.

   • Each normal form must satisfy the previous forms.
   • Use candidate keys and column dependencies to decide how to split tables.
   • Link the resulting tables with foreign keys.
   • Normalization reduces insert, update, and delete problems, but queries may need more joins.

   CodeCopy

   1NF: One row per product in an order.
   OrderLines(OrderID, ProductID, CustomerID, CustomerName, Quantity)
   Key: (OrderID, ProductID). OrderID determines CustomerID; CustomerID determines CustomerName.
   2NF: Move customer details, which depend only on OrderID.
   Orders(OrderID, CustomerID, CustomerName)
   OrderLines(OrderID, ProductID, Quantity)
   3NF: Move CustomerName, which depends on CustomerID.
   Orders(OrderID, CustomerID)
   Customers(CustomerID, CustomerName)
   OrderLines(OrderID, ProductID, Quantity)

   What the interviewer checks: The interviewer checks whether you can use keys and dependencies to split tables and avoid inconsistent data.

   Other ways it was asked

   • “Can you give a practical example of how database normalization is applied?”
   • “What are the first three normal forms in database normalization?”
   • “Can you explain the first three normal forms in database normalization?”

2. When would you denormalize a database, and what trade-offs would you consider?

   Asked in 3 of 274 interviews · last asked Sep 5 · Concept · Mid-level

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   I would denormalize when measured read performance problems justify storing duplicate or precomputed data, such as totals for frequent reports. I would first check whether indexes or query changes solve the problem. The trade-offs are extra storage, more work on writes, and the risk of stale or inconsistent data.

   • Useful for read-heavy reports, dashboards, and queries with costly joins.
   • Faster reads can come at the cost of slower, more complex writes.
   • Define how duplicate data stays in sync and how much delay is acceptable.
   • Measure the benefit against the added storage and maintenance work.

   What the interviewer checks: The interviewer is checking whether you can justify denormalization with workload needs and manage its consistency costs.

   Other ways it was asked

   • “When would you intentionally denormalize a data model?”
   • “In what real world scenarios would you intentionally denormalize a database?”
   • “What are some caveats of denormalizing tables?”

3. When modeling a new table in PostgreSQL, how do you decide between a natural key and a surrogate key, such as BIGSERIAL or UUID, and what performance or operational trade-offs drive that choice?

   Asked in 2 of 274 interviews · last asked Jul 27 · Concept · Senior

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   I use a natural key when it is small, stable, and reliably unique. Otherwise, I use a surrogate key and enforce business uniqueness separately. BIGINT identity or BIGSERIAL gives compact indexes and mostly sequential inserts. UUIDs allow independent ID generation across systems, but use more space and, when random, have poorer index locality.

   • Changing a natural primary key can require updates to foreign keys in other tables.
   • UUID uses 16 bytes; BIGINT uses 8, affecting indexes and foreign key columns.
   • Identity and BIGSERIAL use sequences: gaps are normal, and imports may require resetting the sequence.
   • Time-ordered UUIDs improve index locality compared with random UUIDs, but remain larger than BIGINT.

   What the interviewer checks: The interviewer checks whether you balance business uniqueness, key stability, database performance, and ID generation across systems.

   Other ways it was asked

   • “When you are designing tables in PostgreSQL, what factors make you choose a UUID primary key versus a big serial or identity key?”

4. What relationship types are available in Dynamics 365?

   Asked in 2 of 274 interviews · last asked Apr 16 · Concept · Junior

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   In Dynamics 365 apps that use Dataverse, entity relationships are one-to-many (1:N), many-to-one (N:1), and many-to-many (N:N). Many-to-one is a one-to-many relationship viewed from the other side. One-to-many uses a lookup column, while native many-to-many uses an intersect table.

   • One-to-many: one account can have many contacts; the lookup is on the contact.
   • Many-to-one: many contacts can link to the same account.
   • Many-to-many: records on both sides can have multiple links, such as users and security roles.

   What the interviewer checks: The interviewer checks whether you understand relationship direction and how Dataverse links records.

   Other ways it was asked

   • “What types of entity relationships are available in Microsoft Dynamics 365?”

5. What are data models typically used for?

   Asked in 2 of 274 interviews · last asked Oct 6 · Concept · Junior

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   Data models describe how data is organized, how items relate, and what rules the data must follow. They help teams agree on business needs and design databases for storing, querying, and reporting data. They also guide changes as those needs grow.

   • Use a conceptual model to agree on main business concepts and relationships.
   • Use a logical model to define detailed entities, attributes, keys, and relationships without choosing a specific database.
   • Use a physical model to define storage details, such as tables, columns, and indexes, for a chosen database.

   What the interviewer checks: The interviewer checks whether you can connect data models to business needs and explain their main levels.

   Other ways it was asked

   • “What types of data models are commonly used, and when would you choose each?”
   • “What are data models?”

6. What is an ER diagram?

   Asked in 2 of 274 interviews · last asked Jul 19 · Concept · Junior

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   An ER diagram, or entity-relationship diagram, shows the entities in a data model, their attributes, and how they relate. It also shows how many instances of one entity can relate to another. It helps explain and plan a database structure before building it.

   • Entities represent things such as customers or orders; attributes describe them.
   • Relationships show how entities connect.
   • Cardinality shows one-to-one, one-to-many, or many-to-many relationships.
   • Optionality shows whether a relationship is required or optional.

   CodeCopy

   Customer (customer_id, name)
   Order (order_id, order_date, customer_id)
   One customer can have zero or many orders.
   Each order belongs to exactly one customer.

   What the interviewer checks: The interviewer is checking whether you understand the main parts of an ER diagram and its role in database design.

7. What is a dataset?

   Asked in 2 of 274 interviews · last asked Oct 4 · Concept · Junior

   Other ways it was asked

   • “What is a data set?”

8. What is the business purpose of turning customer activity into structured database fields?

   Asked once · last asked Jul 22 · Concept · Mid-level

   Other ways it was asked

   • “What is the purpose of compressing customer activity into structured database fields?”
   • “What is the purpose of compressing customer information into structured database data?”
   • “What is the business purpose of turning customer activity into structured data?”

9. How would you apply data modeling techniques in an analytics project, and how would you assess their impact on the outcome?

   Asked once · last asked Feb 13 · Behavioral · Senior

   Other ways it was asked

   • “How did you use data modeling techniques in a recent analytics project, and what impact did they have on the project outcome?”

10. In a one-to-many relationship between profiles and phone numbers, which table should contain the foreign key?

    Asked once · last asked Feb 23 · Concept · Junior

11. How would you prevent the same phone number from being assigned to multiple user profiles?

    Asked once · last asked Feb 23 · Scenario · Mid-level

12. What is the difference between structured and unstructured data?

    Asked once · last asked Mar 28 · Concept · Junior

13. When creating a one-to-many relationship, what relationship behaviors can you specify?

    Asked once · last asked Apr 4 · Concept · Mid-level

14. If an entity has a unique attribute, such as a passport number, should you still create a separate primary key?

    Asked once · last asked Apr 27 · Concept · Mid-level

15. How can you implement a one-to-one relationship between two database tables?

    Asked once · last asked Apr 27 · Concept · Mid-level

16. What is the difference between identifying and non-identifying relationships in data modeling?

    Asked once · last asked May 16 · Concept · Junior

17. How do you apply normalization when designing a relational data model?

    Asked once · last asked May 16 · Concept · Junior

18. Is storing multiple related IDs in an array really the best way to model a many-to-many relationship?

    Asked once · last asked Jul 17 · Concept · Mid-level

    Other ways it was asked

    • “What is a better database design for representing many-to-many relationships than storing related IDs in an array?”
    • “What alternative to storing multiple related IDs in an array would you use to model these relationships?”

19. Why can storing related IDs in an array cause problems when modeling relationships between medical records and thesaurus entries?

    Asked once · last asked Jul 17 · Concept · Mid-level

20. When related IDs are stored in an array, what are the implications for saving data and handling cascading deletes?

    Asked once · last asked Jul 17 · Scenario · Mid-level

21. What is a join table, and when would you use one?

    Asked once · last asked Jul 17 · Concept · Junior

22. What risks or problems can arise when using join tables to represent relationships between records?

    Asked once · last asked Jul 17 · Scenario · Mid-level

    Other ways it was asked

    • “What risks or problems can arise when using join tables to represent these relationships?”

23. Surrogate keys vs natural keys: when would you choose each?

    Asked once · last asked Aug 23 · Concept · Mid-level

24. What are the common data modeling relationship types and cardinalities?

    Asked once · last asked Sep 2 · Concept · Mid-level

25. What is the difference between third normal form and Boyce-Codd normal form?

    Asked once · last asked Sep 5 · Concept · Mid-level

26. How do you handle a many-to-many relationship?

    Asked once · last asked Sep 15 · Concept · Mid-level

27. In PostgreSQL specifically, how do nulls behave under a unique constraint, and what implication does that have for modeling optional fields that should be unique when present?

    Asked once · last asked Sep 21 · Concept · Mid-level

28. How would you implement a many-to-many relationship in PostgreSQL?

    Asked once · last asked Sep 30 · Concept · Mid-level

29. What criteria do you use to classify data as big data?

    Asked once · last asked Oct 12 · Concept · Mid-level

30. Is there a cutoff or threshold value above which data is considered big data?

    Asked once · last asked Oct 12 · Concept · Mid-level

31. Why would you use a one-to-many relationship to model a contract's details and installments?

    Asked once · last asked Oct 21 · Concept · Mid-level

    Other ways it was asked

    • “Why did you use a One-to-Many relationship for the contract details and installments?”

32. What is the difference between metadata and data?

    Asked once · last asked Oct 22 · Concept · Junior

33. How does normalization apply to NoSQL databases?

    Asked once · last asked Oct 23 · Concept · Mid-level

34. What is a codebook?

    Asked once · last asked Mar 10 · Concept · Junior

35. What identifier can be used to link a campaign to a finance record?

    Asked once · last asked Mar 17 · Scenario · Mid-level

36. Can you differentiate a data flow diagram (DFD) from an ER diagram?

    Asked once · last asked Mar 27 · Concept · Junior

37. Should the amount field be stored as a String or as a numeric type?

    Asked once · last asked Jul 16 · Concept · Junior

38. When designing a database schema, how do you distinguish business constraints from technical constraints?

    Asked once · last asked Jul 17 · Concept · Mid-level

39. What is an entity in a database?

    Asked once · last asked Jul 19 · Concept · Junior

40. Explain one-to-one, one-to-many, and many-to-many relationships.

    Asked once · last asked Jul 19 · Concept · Junior

41. Who is typically responsible for designing a project's data model?

    Asked once · last asked Aug 2 · Concept · Mid-level

42. What is metadata, and how would you add it to a data system?

    Asked once · last asked Aug 3 · Concept · Mid-level

43. What does a relationship represent in a DBMS?

    Asked once · last asked Aug 26 · Concept · Junior

44. What is structured data, and what does it mean to structure data?

    Asked once · last asked Sep 3 · Concept · Junior

45. What is a surrogate key?

    Asked once · last asked Sep 4 · Concept · Junior

46. What defines a data set, and what are its key characteristics?

    Asked once · last asked Sep 4 · Concept · Junior

47. What is database design?

    Asked once · last asked Sep 9 · Concept · Junior

    Other ways it was asked

    • “What is a database design?”

48. What belongs in a data dictionary?

    Asked once · last asked Sep 18 · Concept · Junior

49. What are the two major types of data modeling?

    Asked once · last asked Sep 22 · Concept · Junior

50. What is normalization, and what are the different forms of normalization?

    Asked once · last asked Oct 7 · Concept · Junior

51. What are the different types of database relationships?

    Asked once · last asked Oct 15 · Concept · Junior

52. What should someone new to ontology or knowledge graph creation understand before contributing effectively?

    Asked once · last asked Oct 23 · Concept · Junior

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How this list is made

Every question here was asked by a real interviewer in a real job interview that a candidate ran MeetAssist in. After the call, the interviewer's questions are pulled from the transcript. Practice sessions, tests, exams and anything that was not a job interview are dropped.

Questions are rewritten so they make sense on their own: names of people, employers and clients are removed, and speech-to-text mistakes are fixed. Small talk, logistics and questions about one candidate's own résumé are left out. Rephrasings of the same question are merged, and the count is the number of different interviews it came up in.

The interviews come from candidates who use MeetAssist, so they lean towards software, data and AI roles: the shares describe these interviews, not every Data Modeling interview. Answers to the most asked questions are written and checked by an editor; a "common mistake" is shown only when reviews of real answers in these interviews show it, with the count.

274 interviews, 168 candidates, Dec 2025 to Oct 2026. Updated every month with new interviews.