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Updated weekly · Last refresh Oct 17

66degrees Data Engineer Interview Questions

The questions to prepare for a 66degrees Data Engineer interview. Questions from real interview reports rank first. Updated daily.

30questions
~4htotal time
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1
SQL & Data ManipulationStart here. 6 questions + 1 drill · ~64 min
Top Customers by Sales RevenueEasy
Practice

Use GROUP BY and SUM to rank the top 10 customers by total revenue from a single sales table.

RankingGroup ByAggregations66degrees
OLTP vs OLAP Database DesignMedium

Explain OLTP vs OLAP designs, including schema shape, workload patterns, and when each is appropriate in a data platform.

financial dataperformanceData Modeling66degrees
Optimize SQL Query PerformanceHard
Practice

Optimize a PostgreSQL reporting query by reducing intermediate rows, using appropriate joins, and calculating monthly performance efficiently.

database optimizationdatabase managementindexes66degrees
Monthly Sales Trends by CategoryMedium
Practice
Practice drill

Aggregate monthly sales by product category and use LAG to calculate month-over-month changes.

InfrastructureToolsData WranglingTotal Wine & MoreInc.Benjamin Moore
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2
Pipelines20 questions · ~179 min
Diagnose Slow Dashboard PipelinesEasy

Approach for finding and fixing a slow dashboard pipeline, from source ingestion to warehouse queries.

InfrastructureToolsQuality66degrees
Clean Data for Visual AnalyticsEasy

Describe how you clean and preprocess data so dashboards stay accurate and usable.

Data WranglingETLQuality66degrees
Design Real-Time Operations Dashboard PipelineHard

Design a pipeline for a real-time operational dashboard, covering streaming ingestion, modeling, data quality, and dashboard serving.

InfrastructureStream ProcessingQuality66degrees
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3
Coding4 questions · ~36 min
Choosing Data Structures for TasksMedium

Tests your ability to select appropriate data structures for performance and correctness.

Hash TablesQueueHeap66degrees
Streaming Data Processing in PythonHard

Tests your ability to design Python code for streaming ingestion and processing patterns.

Hash TablesQueueArrays66degrees
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The finish line: interview-readyComplete all 30 questions plus 1 hands-on drill to finish this plan.