Stripe
Medium
Data ScientistWrite SQL to monitor weekly chargeback spikes
Data Manipulation (SQL/Python)
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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.
171Questions
45Companies
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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Amazon
Medium
Data ScientistDesign student–course data models and SQL
Data Manipulation (SQL/Python)
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October 13, 2025
Amazon
Medium
Data ScientistCompute join counts and window ranks
Data Manipulation (SQL/Python)
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0
October 13, 2025
Block (Square)
Medium
Data ScientistWrite left-join queries with tricky filters
Data Manipulation (SQL/Python)
0
0
October 13, 2025
Other
Medium
Data ScientistSolve window-function SQL without joins
Data Manipulation (SQL/Python)
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0
October 13, 2025
Amazon
Medium
Data ScientistDiagnose MySQL joins and GROUP BY/HAVING errors
Data Manipulation (SQL/Python)
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0
October 13, 2025
Fannie Mae
Medium
Data ScientistAssess SQL joins, unions, windows, dedup, and pandas
Data Manipulation (SQL/Python)
0
0
October 13, 2025
ByteDance
Medium
Data ScientistSelect max-discount product per category
Data Manipulation (SQL/Python)
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0
October 13, 2025
Fetch Rewards
Medium
Data ScientistWrite SQL to verify quarterly sales decline
Data Manipulation (SQL/Python)
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October 13, 2025
SIG (Susquehanna)
Medium
Data ScientistWrite SQL for deliveries analytics
Data Manipulation (SQL/Python)
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October 13, 2025
Two Sigma
Medium
Data ScientistAnalyze NYC taxi trips efficiently over last 7 days
Data Manipulation (SQL/Python)
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October 13, 2025
Instacart
Medium
Data ScientistWrite SQL to rank advertisers and profitability
Data Manipulation (SQL/Python)
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October 13, 2025
Citadel
Medium
Data ScientistImplement left join on Python lists, no packages
Data Manipulation (SQL/Python)
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0
October 13, 2025
Gemini
Medium
Data ScientistWrite SQL/Python for ACH fraud analytics
Data Manipulation (SQL/Python)
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0
October 13, 2025
Meta
Medium
Data ScientistCompute video-call SQL metrics with edge cases
Data Manipulation (SQL/Python)
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October 13, 2025
Meta
Medium
Data ScientistCompute CTR overall and by campaign type
Data Manipulation (SQL/Python)
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October 13, 2025
Meta
Medium
Data ScientistWrite SQL to analyze group-call concurrency
Data Manipulation (SQL/Python)
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October 13, 2025
Meta
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Data ScientistCompute unconnected 60s posts and reactions averages
Data Manipulation (SQL/Python)
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October 13, 2025
Meta
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Data ScientistWrite SQL for visibility, calls, and cohort activity
Data Manipulation (SQL/Python)
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October 13, 2025
Amazon
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Data ScientistAppend country tables and rank salaries in USD
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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.