Cognizant Interview Questions 2026
Published July 22, 2026 · Updated July 22, 2026
6 real interview questions asked at Cognizant. Covers Data Engineering / PySpark, SQL / Joins, SQL / Indexing, SQL / Normalization, SQL / Window Functions, SQL / Query Optimization. Reported by engineers who went through the Cognizant process.
6 questions
141 engineers asked
205 upvotes
Data Engineering / PySpark (1)
Cognizant
Medium
Technical round
3–5 YearsPython
What is the difference between cache() and persist() in Spark? When should you use StorageLevel.MEMORY_AND_DISK?
↑ 76 upvotes · 59 engineers asked this · Data Engineer
SQL / Joins (1)
Cognizant
Easy
Technical round
0-3 yearsSQL
Explain the difference between INNER JOIN, LEFT JOIN, and FULL OUTER JOIN with a simple example of Orders and Customers tables.
↑ 30 upvotes · 22 engineers asked this · Developer
SQL / Indexing (1)
Cognizant
Medium
Technical round
2-5 yearsSQL
A SELECT query filtering on a non-indexed column takes 8 seconds on a 10 million row table. Would adding an index always help? What's the trade-off of adding too many indexes?
↑ 26 upvotes · 15 engineers asked this · Developer
SQL / Normalization (1)
Cognizant
Medium
Technical round
1-4 yearsSQL
What problem does database normalization (1NF, 2NF, 3NF) actually solve? Give an example of an update anomaly in an unnormalized table.
↑ 21 upvotes · 12 engineers asked this · Developer
SQL / Window Functions (1)
Cognizant
Hard
Technical round
2-6 yearsSQL
Write a query to find, for each department, the employee with the second-highest salary, using window functions instead of a correlated subquery.
↑ 33 upvotes · 25 engineers asked this · Developer
SQL / Query Optimization (1)
Cognizant
Medium
Technical round
2-5 yearsSQL
How would you find out why a specific SQL query is slow before making any changes to it?
↑ 19 upvotes · 8 engineers asked this · Developer
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Frequently asked questions
What is the difference between cache() and persist() in Spark? When should you use StorageLevel.MEMORY_AND_DISK?
What is the difference between cache() and persist() in Spark? When should you use StorageLevel.MEMORY_AND_DISK?
Explain the difference between INNER JOIN, LEFT JOIN, and FULL OUTER JOIN with a simple example of Orders and Customers tables.
Explain the difference between INNER JOIN, LEFT JOIN, and FULL OUTER JOIN with a simple example of Orders and Customers tables.
A SELECT query filtering on a non-indexed column takes 8 seconds on a 10 million row table. Would adding an index always help? What's the trade-off of adding too many indexes?
A SELECT query filtering on a non-indexed column takes 8 seconds on a 10 million row table. Would adding an index always help? What's the trade-off of adding too many indexes?
What problem does database normalization (1NF, 2NF, 3NF) actually solve? Give an example of an update anomaly in an unnormalized table.
What problem does database normalization (1NF, 2NF, 3NF) actually solve? Give an example of an update anomaly in an unnormalized table.
Write a query to find, for each department, the employee with the second-highest salary, using window functions instead of a correlated subquery.
Write a query to find, for each department, the employee with the second-highest salary, using window functions instead of a correlated subquery.