SQL (Structured Query Language) is commonly used in data-related job interviews, particularly for roles involving data analysis, data science, database management, or backend development. Here are some practical SQL interview questions that can test a variety of skills:
SQL Practical Interview Questions
- Basic Queries:
- Write a SQL query to find the second highest salary from the ’employees’ table.
- How would you retrieve all the unique values in the ‘department’ column from the ’employees’ table?
- Join Operations:
- Can you create a SQL query that joins two tables, ’employees’ and ‘departments’, and retrieves employee names along with the names of their departments?
- Explain the difference between INNER JOIN, LEFT JOIN, and RIGHT JOIN with examples.
- Aggregate Functions:
- How would you find the average salary in each department of a company?
- Write a query to count the number of employees in each department and display the department name as well.
- Subqueries and Nested Queries:
- Can you write a SQL query to find the names of employees who earn more than the average salary in their department?
- How would you find the department with the highest number of employees using a subquery?
- Data Manipulation and Transaction:
- Demonstrate how to insert new records into a table.
- Write a SQL transaction to update a record and handle possible errors.
- Window Functions:
- Write a SQL query using a window function to rank employees in each department based on their salaries.
- How would you calculate a running total of salaries in a given department?
- Complex Queries:
- How can you retrieve a list of employees who have not completed any tasks, assuming you have ’employees’ and ‘tasks’ tables?
- Write a SQL query to find the third highest salary in a department using a complex subquery or a CTE (Common Table Expression).
- Optimization and Performance:
- How can you optimize a slow-running query?
- What are indexes, and how do they improve query performance?
- Database Design and Normalization:
- Explain the concept of normalization in database design.
- How would you design a database schema for a basic e-commerce application?
- SQL Variants and Specifics:
- Are there any differences in SQL syntax between MySQL and PostgreSQL that you are aware of?
- How would you write a query to handle NULL values effectively in a dataset?
These questions cover a broad range of SQL concepts and are designed to assess both basic knowledge and advanced skills. It’s also important to be ready to explain your thought process and reasoning as you answer.
Conclusion
By familiarizing yourself with these practical SQL interview questions and their answers, you will be well-prepared to tackle any SQL-related challenge during your job interview. Remember to practice these questions and gain hands-on experience to showcase your expertise, authority, and trust in the field of SQL. Good luck with your interview!
