Head Digital Works Data Scientist Interview Questions and Answers

Q1. What is the difference between Union and Union all ?
Ans. 
Union combines the results of two or more SELECT statements, while Union all includes all rows, including duplicates.
• Union removes duplicate rows from the result set, while Union all includes all rows.

• Union sorts the result set, while Union all does not.

• Union is slower than Union all because it performs a distinct operation.

• Example: SELECT column1 FROM table1 UNION SELECT column1 FROM table2;

• Example: SELECT column1 FRO
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Q2. Which query is more faster , joins or union?
Ans. 
Joins are generally faster than unions.
• Joins are typically faster than unions because they combine data from multiple tables based on a common column, while unions combine data from multiple queries into a single result set.

• Joins can utilize indexes on the columns being joined, which can improve performance.

• Unions involve combining the results of multiple queries, which can be slower as it requires merging and sorting ...read more
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Contained aptitude test with both numericals as well as coding questions

It was a one on one round

Q1. Final discussion
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Q2. If ready to relocate
Ans. 
Yes, I am open to relocation for the right opportunity.
• I am willing to relocate for a job that aligns with my career goals and offers growth opportunities.

• I am open to exploring new cities and cultures.

• I understand that relocation may come with some challenges, but I am prepared to face them.

• I am excited about the prospect of working with a new team and contributing to the success of the company.
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Q1. Question about customer retention on sql
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Q2. Joints in depth questions
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Q1. Which algorithm will you prefer from Random Forest and XGBoost when the model is low bias?
Ans. 
XGBoost is preferred over Random Forest for low bias models due to its ability to reduce bias further.
• XGBoost is a more complex algorithm compared to Random Forest, allowing it to reduce bias further in low bias models.

• XGBoost uses gradient boosting which helps in reducing bias by optimizing the loss function iteratively.

• Random Forest may not be able to further reduce bias in low bias models as effectively as XGBoost.

• I...read more
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Q1. Technical questions about machine learning and data science
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Q1. Machine learning and data science and about past industry projects
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Q1. Salary discussion and about joining. Roles explained by HR
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