Important Data Analytics Interview Questions and Answers
Prepare for your next job with Important Data Analytics Interview Questions and Answers. Get expert insights on key topics and boost your interview success!
Python for Data Analytics
1. What are Python’s key libraries for data analytics?
Pandas, NumPy, Matplotlib, Seaborn, Scikit-learn, Statsmodels.
2. What is Pandas and why is it useful in data analysis?
Pandas is a data manipulation library that provides DataFrame and Series structures for handling and analyzing structured data.
3. How do you handle missing data in Pandas?
Using .dropna() to remove missing values or .fillna(value) to fill them with a specific value.
4. What is the difference between apply() and map() in Pandas?
map() works on Series, while apply() works on both Series and DataFrames for element-wise operations.
5. How do you merge two datasets in Pandas?
Using merge(), concat(), or join() based on keys and indexes.
6. How to group data in Pandas?
Using groupby() and applying aggregation functions like sum(), mean(), count().
7. What are NumPy arrays, and how do they differ from Python lists?
NumPy arrays are more efficient, support vectorized operations, and consume less memory.
8. How to reshape a NumPy array?
Using .reshape(rows, cols) or .ravel() to flatten.
9. What is the difference between a pivot table and a groupby operation?
Pivot tables allow dynamic reshaping, whereas groupby() aggregates values based on a specific column.
10. How do you detect and remove duplicate values in Pandas?
Using .duplicated() to find duplicates and .drop_duplicates() to remove them.
11. Explain the difference between iloc[] and loc[] in Pandas.
iloc[] is used for positional indexing, while loc[] is used for label-based indexing.
12. How to handle categorical data in Python?
Using one-hot encoding (pd.get_dummies()) or label encoding (sklearn.preprocessing.LabelEncoder()).
13. How do you optimize large datasets in Pandas?
Using dtype optimization, chunking (read_csv(chunksize=10000)), and using categorical data types.
14. What is the difference between .apply() and .transform()?
.apply() applies a function and returns aggregated results, whereas .transform() retains the same shape as the original DataFrame.
15. Explain broadcasting in NumPy.
Broadcasting allows operations between arrays of different shapes by automatically expanding smaller arrays.
SQL for Data Analytics
16. What is SQL?
SQL (Structured Query Language) is used for managing and querying relational databases.
17. What is the difference between WHERE and HAVING?
WHERE filters rows before aggregation, while HAVING filters groups after aggregation.
18. What are the different types of joins in SQL?
INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN, CROSS JOIN.
19. How do you fetch the top N records from a table?
Using LIMIT N in MySQL/PostgreSQL and TOP N in SQL Server.
20. What is the difference between COUNT(*), COUNT(column), and COUNT(DISTINCT column)?
COUNT(*) counts all rows, COUNT(column) counts non-null values, COUNT(DISTINCT column) counts unique values.
21. What is a primary key and a foreign key?
A primary key uniquely identifies a row, while a foreign key establishes a relationship between two tables.
22. How do you retrieve the second-highest salary from a table?
SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees);
23. What is the difference between RANK(), DENSE_RANK(), and ROW_NUMBER()?
RANK() allows gaps in ranking, DENSE_RANK() does not, ROW_NUMBER() assigns a unique number to each row.
24. What is the difference between UNION and UNION ALL?
UNION removes duplicates, while UNION ALL includes all rows.
25. How do you find duplicate records in a table?
SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name HAVING COUNT(*) > 1;
26. What are window functions in SQL?
Functions like ROW_NUMBER(), RANK(), LEAD(), LAG() used for analytics.
27. Explain Common Table Expressions (CTEs).
WITH cte AS (SELECT * FROM table_name) SELECT * FROM cte;
28. What are indexes in SQL, and why are they important?
Indexes improve query performance by allowing faster searches.
29. What is the difference between DELETE, TRUNCATE, and DROP?
DELETE removes rows with conditions, TRUNCATE removes all rows, DROP removes the table itself.
30. What is a stored procedure?
A set of SQL statements stored and executed on the database server.
Power BI for Data Analytics
31. What is Power BI?
A business intelligence tool used for data visualization and reporting.
32. What are the key components of Power BI?
Power Query, Power Pivot, Power View, Power Map, Power BI Service.
33. What are the different types of filters in Power BI?
Page-level, report-level, and visual-level filters.
34. What is the difference between Power BI Desktop and Power BI Service?
Desktop is for development; Service is for sharing and collaboration.
35. What is a measure in Power BI?
A DAX formula is used to perform calculations dynamically.
36. What is the difference between calculated columns and measures?
Calculated columns store data in the model; measures are computed dynamically.
37. How do you create relationships between tables in Power BI?
Using the Model tab to define one-to-many, one-to-one, or many-to-many relationships.
38. What is DAX?
Data Analysis Expressions, a formula language used in Power BI.
39. How do you optimize Power BI performance?
Reducing data size, optimizing DAX calculations, and using aggregations.
40. What is DirectQuery vs. Import Mode?
Import loads data into Power BI, and DirectQuery queries the database in real-time.
41. What are bookmarks in Power BI?
They capture the current state of a report for navigation.
42. What is the purpose of drill-through in Power BI?
Allows users to navigate from a summary to a detailed view.
43. What are the parameters of Power BI?
User-defined inputs that dynamically modify reports.
44. How can you share Power BI reports securely?
Using Power BI Service with role-based access control.
45. What is Row-Level Security (RLS) in Power BI?
Restricts data access based on user roles.
46. What is normalization in SQL?
Normalization is the method used to streamline data storage within a database, reducing redundancy and enhancing data integrity. This approach entails dividing tables into more manageable, interrelated tables and establishing connections between them.
47. What is a self-join, and how would you use it?
A self-join is a type of join where a table is joined with itself. It is useful when creating relationships within the same table, such as finding hierarchical relationships or comparing rows with related data.
48. Discuss SQL server reporting services.
SQL Server Reporting Services is a reporting tool provided by Microsoft for creating, managing, and delivering interactive, tabular, graphical, and free-form reports. SSRS allows users to design and generate reports from various data sources, making it a valuable asset for businesses needing comprehensive reporting capabilities.
49. What are ctes (Common table expressions)?
Common Table Expressions (CTEs) serve as momentary result sets that you can mention within SQL statements, typically found within SELECT, INSERT, UPDATE, or DELETE operations. They’re established using the `WITH` keyword and are instrumental in streamlining intricate queries by dividing them into more digestible components.
50. Explain the MERGE statement.
The SQL MERGE statement is employed to execute insertions, updates, or deletions on a target table, guided by the outcomes of a source table or query. It consolidates the functionalities of several individual statements (INSERT, UPDATE, DELETE) into one comprehensive statement, rendering it particularly valuable for achieving data synchronization between tables.
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