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What types of queries would not be efficient in Athena?

Cloud/Toolshard0.4 min readPremium
Frequency
Low
Asked at 1 company
Category
179
questions in Cloud/Tools
Difficulty Split
104E|27M|48H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Capco
Key Concepts Tested
joinoptimizationpartition
Expert AnswerPremium
87 wordsInterview-ready
**Athena economics**: $5/TB scanned—inefficient queries burn budget. **Inefficient patterns**: (1) Full table scans on unpartitioned data—always partition. (2) Many small files—each incurs metadata overhead; coalesce to 128MB+ Parquet. (3) SELECT *—scan only needed columns. (4) Complex joins without partition pruning—filter early. (5) Cross joins, Cartesian products. (6) UDFs on every row. (7) OLTP-style point lookups—use RDS. **Why**: Athena is for analytical scans; it's not a database....
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 Capco. The answer also includes follow-up discussion points that interviewers commonly explore.

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