Database Fundamentals and Data Modeling Questions

Encompasses foundational database concepts and techniques for designing and querying data stores. Topics include relational database concepts, structured query language fundamentals for selecting and modifying data, schema design with tables and relationships, normalization principles, entity relationship modeling, indexing and basic performance considerations, transactions and data integrity, constraints and data types, and common operational tasks such as migrations, backups, and simple optimization strategies. Also discusses trade offs with nonrelational stores and when to choose different persistence models.

EasyTechnical

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What is a write-ahead log (WAL) and why do many databases use it? Explain how WAL enables durability, crash recovery, supports replication, and enables point-in-time restore in common RDBMS designs.

HardTechnical

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Compare conflict resolution techniques in eventually-consistent systems: last-write-wins (LWW), vector clocks, and CRDTs. For each approach describe how conflicts are detected, how resolution is performed, types of data/operations suited for the method, and operational complexity.

EasyTechnical

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Write a SQL query (PostgreSQL) to select the top 3 most recent orders per customer from an orders table with schema: orders(order_id INT PK, customer_id INT, total_amount NUMERIC, created_at TIMESTAMP). Explain how you handle ties when two orders have the same created_at and state any assumptions about indexing and performance.

MediumTechnical

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Compare built-in full-text search in PostgreSQL (tsvector/tsquery) with an external search engine such as Elasticsearch. Discuss indexing, scoring and relevancy tuning, scaling, consistency, and operational overhead. For product search with typos and facets, which would you choose and why?

EasyTechnical

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Discuss the trade-offs between enforcing referential integrity at the database level versus in application code. Cover correctness, performance, scalability, and operational complexity for each approach and the scenarios where one is preferred over the other.

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