Real questions from top companies in SQL · medium
Explain CTE vs Temp Table. What are the differences and use cases?
Explain Data Modeling SCD Types (Type 1, 2, 3).
Implement a recursive query for hierarchy (employee-manager). Explain the termination guarantees, depth limits, and when a recursive CTE becomes a scalability bottleneck. What alternatives exist for graph-scale hierarchies in Spark or a data lake?
Compare Glue partition discovery with Hive MSCK/ADD PARTITION. Explain the operational and cost implications of crawler-based vs. partition-projection approaches. When does partition projection become necessary, and what are its limitations?
Explain how partitioning and bucketing in Hive/Spark optimize queries. What are the trade-offs in bucket count, partition cardinality, and small-file problem? When does over-partitioning or over-bucketing become counterproductive?
Explain the concept of window functions in SQL and provide an example
Explain the difference between Star and Snowflake schemas. When would you choose one over the other?
Explain the difference between partition count and query performance in Spark.
How would you handle data type changes for an existing column?
How would you handle duplicate or corrupted data in a batch ETL job?
How would you handle nulls in a SQL join? Provide examples using COALESCE.
How would you identify duplicate records based on a composite key in SQL?
How would you optimize a query fetching sales data across multiple countries with billions of rows?
How would you optimize a query with multiple joins and subqueries?
How would you prevent small file problems in S3 when loading data into Redshift?
How would you retrieve the first and last order for each customer from a sales table?
Identify and remove duplicate records from a table, keeping the most recent record based on a timestamp column.
If manual partitions are created in a Hive data-warehouse table directory, and you query records from those partitions, will you see the data? If not, how can this be fixed?
Implement a CASE WHEN condition - medium difficulty
Kafka Partitioning: How would you ensure even load distribution across Kafka partitions in a high-volume system?
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