Robinhood
Medium
Data ScientistWrite SQL and Python for transaction analytics
Data Manipulation (SQL/Python)
4
0
October 13, 2025
SQL JOIN Interview Questions
SQL JOIN questions test whether you can combine data across tables while preserving the right grain and relationships. Expect INNER, LEFT, RIGHT, CROSS, and FULL OUTER JOINs, plus multi-table joins and JOIN + aggregation patterns.
169Questions
43Companies
Easy 0 • Medium 169 • Hard 0Difficulty mix
Common SQL JOIN interview patterns
- INNER vs LEFT JOIN logic
- Anti-joins (find missing records)
- Self-joins for comparisons within a table
- JOIN + GROUP BY for aggregated results
- Conditional joins with additional predicates
- Multi-key joins across composite keys
- Deduplication using JOINs
SQL JOIN interview questions
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Citadel
Medium
Data ScientistImplement left join on Python lists, no packages
Data Manipulation (SQL/Python)
4
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October 13, 2025
Capital One
Medium
Data ScientistMerge four CSVs locally, robustly and efficiently
Data Manipulation (SQL/Python)
4
0
October 13, 2025
Amazon
Medium
Business Intelligence EngineerAnalyze Top Book Sales and Unique Customer Purchases
Data Manipulation (SQL/Python)
8
0
July 12, 2025
Block (Square)
Medium
Data ScientistWrite left-join queries with tricky filters
Data Manipulation (SQL/Python)
3
0
October 13, 2025
Meta
Medium
Data ScientistDetermine Product Buyer Count and Interaction Percentage
Data Manipulation (SQL/Python)
9
0
July 12, 2025
Meta
Medium
Data ScientistCalculate posts per DAU by country today
Data Manipulation (SQL/Python)
3
0
October 13, 2025
Capital One
Medium
Data ScientistMerge CSVs and build revenue pivot with pandas
Data Manipulation (SQL/Python)
3
0
October 13, 2025
Coinbase
Medium
Data ScientistWrite SQL: sum values ≤ each row’s value
Data Manipulation (SQL/Python)
3
0
October 13, 2025
Meta
Medium
Data ScientistCompute feed ad frequency and retention in SQL
Data Manipulation (SQL/Python)
3
0
October 13, 2025
Amazon
Medium
Business Intelligence EngineerCount Customers Buying Both 'Kindle' and 'Alexa'
Data Manipulation (SQL/Python)
10
0
July 12, 2025
Amazon
Medium
Business Intelligence EngineerIdentify Employees with Invalid Department References
Data Manipulation (SQL/Python)
6
0
July 12, 2025
Amazon
Medium
Business Intelligence EngineerIllustrate SQL Join Results with Duplicate Keys
Data Manipulation (SQL/Python)
7
0
July 12, 2025
CVS Health
Medium
Data ScientistUse pandas to aggregate, pivot, and label
Data Manipulation (SQL/Python)
2
0
October 13, 2025
Amazon
Medium
Data ScientistCalculate Regional Revenue and Identify Top Customers
Data Manipulation (SQL/Python)
9
0
July 12, 2025
Uber
Medium
Data ScientistCalculate January-2024 SF Promotion Impact Using SQL Queries
Data Manipulation (SQL/Python)
7
0
July 12, 2025
Gemini
Medium
Data ScientistWrite SQL/Python for ACH fraud analytics
Data Manipulation (SQL/Python)
1
0
October 13, 2025
OPPO
Medium
Data EngineerSolve three SQL problems (easy/medium/hard)
Data Manipulation (SQL/Python)
0
0
August 14, 2025
Amazon
Medium
Data ScientistCompute join counts and window ranks
Data Manipulation (SQL/Python)
1
0
October 13, 2025
Other
Medium
Data ScientistDiagnose zero IE uploads with SQL
Data Manipulation (SQL/Python)
1
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October 13, 2025
Common mistakes with SQL JOINs
- JOIN explosion from many-to-many relationships
- Filtering in WHERE instead of ON for LEFT JOINs
- Incorrect NULL handling on optional joins
- COUNT(*) vs COUNT(column) confusion
- Duplicate rows after joins
How JOIN questions are evaluated in interviews
Correctness beats performance; the right result set matters most.
Explain your join keys, assumptions, and how NULLs are treated.
Reasoning and clarity matter more than memorized syntax.
Related SQL concepts
SQL JOIN Interview FAQs
What is the difference between INNER JOIN and LEFT JOIN in interviews?
INNER JOIN returns only matching rows from both tables, while LEFT JOIN keeps all rows from the left table and fills unmatched right rows with NULLs. Interviewers often test whether you choose the correct join for required vs optional relationships.
When should I use a subquery instead of a JOIN?
Use a subquery when you need to filter or aggregate before joining, or when a correlated condition is clearer. JOINs are better for combining row-level data, while subqueries can simplify multi-step logic.