Post #2469

Data Analyst Interview Questions with Answers: Part-2🧠 11. What is a subquery? A subquery is a query nested inside another SQL query (like SELECT, INSERT, UPDATE, DELETE). It returns data used by the outer query. Example: SELECT name FROM students WHERE marks > (SELECT AVG(marks) FROM students); 12. Explain GROUP BY and HAVING clause • GROUP BY: Groups rows by a column's values for aggregation (SUM(), COUNT(), etc.) • HAVING: Filters aggregated results (like WHERE for groups) Example: SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 5; 13. What are window functions in SQL? Window functions perform calculations across a set of rows related to the current row without collapsing rows. Example: ROW_NUMBER(), RANK(), LEAD(), LAG() SELECT name, department, RANK() OVER(PARTITION BY department ORDER BY salary DESC) FROM employees; 14. Difference between RANK(), DENSE_RANK(), ROW_NUMBER() • ROW_NUMBER(): Unique rank even if values are the same • RANK(): Skips ranks for ties • DENSE_RANK(): No rank gaps for ties Example: If two people tie at 2nd place: • RANK: 1, 2, 2, 4 • DENSE_RANK: 1, 2, 2, 3 • ROW_NUMBER: 1, 2, 3, 4 15. What is a CTE in SQL? CTE (Common Table Expression) is a temporary result set defined with WITH for better readability and reuse in a query. Example: WITH HighEarners AS ( SELECT name, salary FROM employees WHERE salary > 100000 ) SELECT * FROM HighEarners; 16. What is the difference between WHERE and HAVING? • WHERE: Filters before grouping (on individual rows) • HAVING: Filters after grouping (on aggregates) Example: SELECT department, COUNT(*) FROM employees WHERE active = 1 GROUP BY department HAVING COUNT(*) > 10; 17. Explain data types in SQL Data types define the kind of data a column can store: • INT, FLOAT – Numeric • VARCHAR, TEXT – Strings • DATE, DATETIME – Time values • BOOLEAN – True/False values 18. How do you handle NULL values in SQL? • Use IS NULL or IS NOT NULL • Use functions like COALESCE() to replace NULLs Example: SELECT COALESCE(phone, 'Not Provided') FROM customers; 19. What are common data visualization tools? • Power BI • Tableau • Google Data Studio • Excel • Python libraries: Matplotlib, Seaborn, Plotly 20. When would you use a bar chart vs pie chart? • Bar chart: Compare multiple categories clearly • Pie chart: Show proportions of a whole (best for 2–5 categories) Bar charts are generally more accurate and readable. 💬Double Tap ♥️ For Part-3