Answer SQL And Data Warehouse Fundamentals For A Data Engineering Interview
You are interviewing for a data engineering role focused on analytical SQL and warehouse modeling. Answer the following multi-part prompt, keeping in mind standard SQL concepts, analytical workloads, and deterministic output.
Part 1 - SQL Set Operations And Anti-Joins
Explain the difference between UNION and UNION ALL. Which one would you choose by default, and why?
Then explain a left anti-join and write three equivalent forms for returning rows in table a that do not have a matching user_id in table b.
Part 2 - Top Sales By County And Year
Given a table uk_price_paid with columns:
| column | type |
|---|---|
date | date or timestamp |
county | string |
price | numeric |
For each county and each year from 2020 through 2022, return exactly three rows with the highest sale prices. If two sales tie on price, either may rank higher, but each county-year should contain exactly three rows when at least three rows exist.
Part 3 - Data Warehouse Modeling Fundamentals
Answer these conceptual questions:
- What is a star schema?
- What are the pros and cons of a star schema compared with one very wide table?
- What is the difference between OLTP and OLAP?
- What are common fact table types?
- How would you model high-volume sensor readings, such as one speed reading per aircraft per second?
- What is a slowly changing dimension?
- How would you model a many-to-many relationship?
AI interview prep
Core dilemma
Balancing the expressiveness and performance of SQL for analytical queries against the need for clear, maintainable, and scalable data warehouse designs.
3 tradeoffs and 3 stress tests locked
Interview prep
Unlock the interviewer X-Ray rubric, tradeoff matrix, stress tests, clarifying questions, and key concepts.
Answer SQL And Data Warehouse Fundamentals For A Data Engineering Interview
You are interviewing for a data engineering role focused on analytical SQL and warehouse modeling. Answer the following multi-part prompt, keeping in mind standard SQL concepts, analytical workloads, and deterministic output.
Part 1 - SQL Set Operations And Anti-Joins
Explain the difference between UNION and UNION ALL. Which one would you choose by default, and why?
Then explain a left anti-join and write three equivalent forms for returning rows in table a that do not have a matching user_id in table b.
Part 2 - Top Sales By County And Year
Given a table uk_price_paid with columns:
| column | type |
|---|---|
date | date or timestamp |
county | string |
price | numeric |
For each county and each year from 2020 through 2022, return exactly three rows with the highest sale prices. If two sales tie on price, either may rank higher, but each county-year should contain exactly three rows when at least three rows exist.
Part 3 - Data Warehouse Modeling Fundamentals
Answer these conceptual questions:
- What is a star schema?
- What are the pros and cons of a star schema compared with one very wide table?
- What is the difference between OLTP and OLAP?
- What are common fact table types?
- How would you model high-volume sensor readings, such as one speed reading per aircraft per second?
- What is a slowly changing dimension?
- How would you model a many-to-many relationship?