To succeed, your preparation must align with the specific technical areas Mphasis prioritizes. The evaluation is heavily weighted toward practical syntax and data manipulation rather than abstract system design.
SQL and Relational Data Manipulation
SQL is the bedrock of data engineering at Mphasis. Interviewers expect you to be fluent in complex querying, data aggregation, and performance optimization. This is not about basic SELECT statements; it is about proving you can manipulate large datasets efficiently.
Be ready to go over:
- Window Functions – Using
ROW_NUMBER(), RANK(), DENSE_RANK(), and LEAD()/LAG() to solve complex analytical problems.
- Advanced Joins and Aggregations – Understanding the nuances of inner, outer, cross, and self joins, along with
GROUP BY and HAVING clauses.
- Performance Tuning – Knowing how to read execution plans, use indexes effectively, and avoid common bottlenecks like Cartesian products.
- Advanced concepts (less common) – Recursive CTEs, pivoting/unpivoting data, and handling complex JSON or XML data within SQL.
Example questions or scenarios:
- "Write a SQL query to find the second highest salary in each department using window functions."
- "Explain the difference between
RANK() and DENSE_RANK() with a practical data example."
- "How would you optimize a query that is joining two massive tables and running too slowly?"
PySpark and Big Data Processing
For modern data engineering roles at Mphasis, PySpark is heavily scrutinized. Based on candidate experiences, interviewers will ask highly specific questions about PySpark syntax, DataFrame operations, and built-in functions. You must know the code, not just the theory.
Be ready to go over:
- DataFrame Operations – Selecting, filtering, dropping, and renaming columns. Exact syntax is frequently tested.
- Transformations vs. Actions – Clear understanding of lazy evaluation and the difference between operations like
map(), filter() (transformations) and collect(), count() (actions).
- PySpark SQL Functions – Utilizing
pyspark.sql.functions for string manipulation, date formatting, and conditional logic (when().otherwise()).
- Advanced concepts (less common) – Broadcast variables, handling data skewness in partitions, and optimizing Spark memory management.
Example questions or scenarios:
- "What is the exact PySpark syntax to add a new column based on a conditional statement?"
- "Explain how you would handle missing or null values in a PySpark DataFrame."
- "Write the PySpark code to perform an inner join between two DataFrames and aggregate the results."
Core Data Engineering & ETL Concepts
While syntax is king, you must also demonstrate a solid understanding of how data moves from source to destination. You will be evaluated on your knowledge of ETL/ELT principles and data warehousing fundamentals.
Be ready to go over:
- Data Warehousing – Differences between Star and Snowflake schemas, and understanding of Fact and Dimension tables.
- Pipeline Architecture – High-level understanding of how to extract data from APIs or databases, transform it, and load it into a target destination.
- Data Quality – Techniques for ensuring data integrity, handling duplicates, and managing schema evolution.
Example questions or scenarios:
- "Describe the difference between an ETL and an ELT pipeline."
- "How do you handle slowly changing dimensions (SCD) in a data warehouse?"
- "What steps do you take to validate data quality after a large batch load?"