Cognizant Data Engineer Interview Questions and Answers

SQL tricky questions often test your understanding of complex queries and data manipulation techniques.

• Understand JOIN types: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN.

• Use GROUP BY and HAVING clauses to aggregate data effectively.

• Be familiar with window functions like ROW_NUMBER(), RANK(), and DENSE_RANK().

• Practice writing subqueries and common table expressions (CTEs) for better readability.

• Know how to h...read more

Different types of joins in Spark include inner join, outer join, left join, right join, and full join.

• Inner join: Returns only the rows that have matching values in both datasets.

• Outer join: Returns all rows when there is a match in either dataset.

• Left join: Returns all rows from the left dataset and the matched rows from the right dataset.

• Right join: Returns all rows from the right dataset and the matched rows f...read more

Delta Lake is an open-source storage layer that brings ACID transactions to Apache Spark and big data workloads.

• Delta Lake provides ACID transactions, scalable metadata handling, and unifies streaming and batch data processing.

• It stores data in Parquet format and uses Apache Spark for processing.

• Delta Lake ensures data reliability and data quality by providing schema enforcement and data versioning.

• It supports tim...read more

To connect S3 from Databricks, you can use the AWS connector provided by Databricks.

• Use the AWS connector provided by Databricks to connect to S3

• Provide the necessary AWS credentials and S3 bucket details in the connector configuration

• You can access S3 data using the file system API in Databricks

XCom in Airflow is a way for tasks to exchange messages or small amounts of data.

• XCom allows tasks to communicate with each other by passing small pieces of data

• It can be used to share information between tasks in a DAG

• XCom can be used to pass information like task status, results, or any other data

CDC stands for Change Data Capture, a process of identifying and capturing changes made to data in a database.

• CDC is used to track changes in data over time, allowing for real-time data integration and analysis.

• It captures inserts, updates, and deletes made to data, providing a historical record of changes.

• CDC is commonly used in data warehousing, data replication, and data integration processes.

• Examples of CDC to...read more

A list in Python is a collection of items that are ordered and mutable.

• Lists are created using square brackets []

• Items in a list can be of different data types

• Lists can be modified by adding, removing, or changing items

• Example: my_list = [1, 'apple', True]

Flat map is used to flatten nested arrays while map is used to transform each element in an array.

• Flat map is used to flatten nested arrays into a single array.

• Map is used to transform each element in an array using a function.

• Flat map is commonly used in functional programming languages like JavaScript and Scala.

• Map is a higher-order function that applies a given function to each element in an array.