Common Interview Questions on SELECT Queries

 

Common Interview Questions on SELECT Queries

Basic Queries

1. How do you retrieve all columns from a table?

2. Write a query to fetch specific columns from a table.

3. How do you rename a column in the result set using an alias?

4. What is the use of the DISTINCT keyword?

Filtering and Conditions

5. Write a query to fetch rows where a column value equals a specific number.

6. How do you filter rows based on a range using BETWEEN?

7. Write a query to search for rows where a column value starts with 'A'.

8. How do you combine multiple conditions in a WHERE clause?

Sorting and Limiting

9. How do you sort rows in descending order?

10. Write a query to fetch the top 5 rows based on a column value.

Joins

11. Explain the difference between INNER JOIN and LEFT JOIN.

12. Write a query to fetch data from two tables using an INNER JOIN.

13. How do you include unmatched rows from one table in the result set?

Aggregations and Grouping

14. How do you calculate the sum of a column?

15. Write a query to count the number of rows in each group.

16. How do you filter groups using the HAVING clause?

Subqueries

17. Explain the difference between correlated and non-correlated subqueries.

18. Write a query to fetch rows where a column value exceeds the average.

Advanced Filtering

19. How do you filter rows using the IN clause?

20. Write a query to exclude rows matching a list of values.

Combining Results

21. What is the difference between UNION and UNION ALL?

22. Write a query to combine results from two queries.

Date and String Functions

23. How do you calculate the difference between two dates?

24. Write a query to concatenate two string columns.

Performance and Optimization

25. How do indexes affect the performance of a SELECT query?

26. Explain the importance of filtering on indexed columns.

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Final Thoughts

This cheat sheet provides a quick reference to the most commonly used SELECT query features in SQL, as well as common interview questions to help you prepare effectively. Whether you're a beginner or a seasoned developer, mastering these queries will enhance your SQL skills and interview readiness. Experiment with these techniques to become a SQL pro!