Nineleaps Technology Solutions Data Analyst Interview Questions, Process, and Tips

Q1. Coalesce, SQL Order of Execution
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Q2. Given a table with fields(id, name, salary, managerId) find out the managers who have atleast 5 reportees under him/her.
Ans. 
Use SQL query to count number of reportees for each manager and filter out those with atleast 5 reportees.
• Write a SQL query to count number of reportees for each manager using GROUP BY clause

• Add HAVING clause to filter out managers with atleast 5 reportees

• Example: SELECT managerId, COUNT(id) AS num_reportees FROM table_name GROUP BY managerId HAVING num_reportees >= 5
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Q3. How to manage large datasets in python
Ans. 
Use libraries like pandas and dask to efficiently manage large datasets in Python.
• Use pandas library for data manipulation and analysis.

• Use dask library for parallel computing and out-of-core processing.

• Optimize memory usage by loading data in chunks or using data types efficiently.

• Consider using cloud services like AWS S3 or Google BigQuery for storing and processing large datasets.
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Q4. Name few of the commonly used python libraries used by DA
Ans. 
Some commonly used Python libraries for Data Analysts are Pandas, NumPy, Matplotlib, and Scikit-learn.
• Pandas - used for data manipulation and analysis

• NumPy - used for numerical computing and working with arrays

• Matplotlib - used for data visualization

• Scikit-learn - used for machine learning and data mining
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Q1. Difference Between Union and Union All
Ans. 
Union combines and removes duplicates, Union All combines without removing duplicates
• Union combines result sets and removes duplicates

• Union All combines result sets without removing duplicates

• Union is slower than Union All as it involves removing duplicates

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

• Example: SELECT column1 FROM table1 UNION ALL SELECT column1 FROM table2;
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Q2. SQL Execution order
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Q3. Coalesce function in SQL
Ans. 
Coalesce function in SQL is used to return the first non-null value in a list of expressions.
• Coalesce function takes multiple parameters and returns the first non-null value.

• It is commonly used to handle null values in SQL queries.

• Example: SELECT COALESCE(column_name, 'N/A') FROM table_name;
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Q1. Basic 10-15btheorotical question
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Q2. Join + window funct question
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Basics of SQL was asked, having good foundation will really help in clearing this round