DataEngPrep.tech
QuestionsBlogStore
Get PDF Bundle
Home/Questions/SQL/How would you optimize a query with multiple joins and subqueries?

How would you optimize a query with multiple joins and subqueries?

SQLmedium0.7 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
American Express
Key Concepts Tested
join
Expert AnswerPremium
144 wordsInterview-ready
Optimizing multi-join/subquery queries: (1) Reduce join cardinality early—filter before joining. (2) Replace correlated subqueries with JOINs: e.g., SELECT * FROM a WHERE a.id IN (SELECT id FROM b WHERE ...) becomes JOIN (SELECT id FROM b WHERE ...) b ON a.id = b.id. (3) Use CTEs for readability and to let optimizer materialize. (4) Ensure join columns are indexed. (5) Join smallest tables first when possible. (6) Avoid SELECT * in subqueries. (7) Use EXPLAIN to detect full scans....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like American Express. The answer also includes follow-up discussion points that interviewers commonly explore.

Continue Reading the Full Answer

Unlock the complete expert answer with code examples, trade-offs, and pro tips - plus 1,863+ more.

Create Free Account - Unlock 30 Answers
Get PDF Bundle - from $21

Or upgrade to Platform Pro - $39

Engineers who used these answers got offers at

AmazonDatabricksSnowflakeGoogleMeta

Free: Top 20 SQL Interview Questions (PDF)

Get the most asked SQL questions with expert answers. Instant download.

No spam. Unsubscribe anytime.

Related SQL Questions

mediumWrite an SQL query to find the second-highest salary from an employee table.FreemediumDemonstrate the difference between DENSE_RANK() and RANK()FreemediumDiscuss differences between ROW_NUMBER(), RANK(), and DENSE_RANK(), and provide examples from your projects.FreemediumExplain the differences between Data Warehouse, Data Lake, and Delta LakeFreemediumExplain the differences between Repartition and Coalesce. When would you use each?Free

According to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

← Back to all questionsMore SQL questions →