Database Analyst: Top Interview SQL Challenges (Solutions)

In the data-driven world of today, the role of a Database Analyst is of prime importance. These professionals act as the custodians of data, ensuring efficient data storage, retrieval, and insightful analysis. Among the core skills expected from any aspiring database analyst, proficiency in Structured Query Language (SQL) ranks at the very top.

Whether you are attending your first interview or your tenth, SQL remains the undisputed champion of technical questioning. Companies want to make sure that database analysts not only understand data but can also manipulate and interpret it using SQL commands. This article takes an in-depth look at the top SQL interview challenges encountered by candidates and provides clear, practical solutions for each to help you stand out in the interview process.

1. Retrieve the Second Highest Salary from a Table

This is one of the classic interview questions that tests your ability to work with subqueries and filtering.

Challenge:

Given a table Employees(emp_id, name, salary), write a query to fetch the second highest salary.

Solution:

SELECT MAX(salary)
FROM Employees
WHERE salary < (SELECT MAX(salary) FROM Employees);

Why it matters: This query demonstrates your ability to think in layers using subqueries effectively to drill deeper into the data.

Alternative Solution Using RANK()

SELECT salary
FROM (
  SELECT salary, RANK() OVER (ORDER BY salary DESC) AS rank
  FROM Employees
) AS RankedSalaries
WHERE rank = 2;

Tip: Using window functions like RANK() or DENSE_RANK() is often considered more robust especially when dealing with duplicate values.

2. Find Duplicate Rows in a Table

Interviewers love this question because it tests your knowledge of grouping, counting, and filtering—core concepts for any database analyst.

Challenge:

Given a table Orders(order_id, product_id, customer_id), find all the customer_id and product_id pairs that appear more than once.

Solution:

SELECT customer_id, product_id, COUNT(*)
FROM Orders
GROUP BY customer_id, product_id
HAVING COUNT(*) > 1;

This query uses GROUP BY in combination with HAVING to filter groups having more than one occurrence—a standard but vital SQL trick.

3. Delete Duplicate Records

The ability to clean data using SQL is crucial. Interviewers assess not just your syntax, but also your understanding of transaction safety and data preservation.

Challenge:

Remove all duplicate rows from a table, keeping only the first occurrence.

Solution Using CTE (Common Table Expression):

WITH CTE AS (
  SELECT *, ROW_NUMBER() OVER (
    PARTITION BY customer_id, product_id
    ORDER BY order_id) AS rn
  FROM Orders
)
DELETE FROM CTE WHERE rn > 1;

Note: Ensure you’re working in a SQL engine that supports deleting from CTEs, such as SQL Server or PostgreSQL.

4. Find Department with the Highest Average Salary

This question combines aggregation, grouping, and subqueries—all the ingredients of intermediate-to-advanced SQL logic.

Challenge:

Given a table Employees(emp_id, name, salary, dept_id), find the department with the highest average salary.

Solution:

SELECT dept_id
FROM Employees
GROUP BY dept_id
ORDER BY AVG(salary) DESC
LIMIT 1;

Alternate with Subquery:

SELECT dept_id
FROM (
  SELECT dept_id, AVG(salary) AS avg_salary
  FROM Employees
  GROUP BY dept_id
) AS DepartmentAvg
ORDER BY avg_salary DESC
LIMIT 1;

Takeaway: Knowing the performance cost of each method helps you choose the best one in real-world scenarios.

5. Understanding NULL in Conditions

One of the subtle challenges in interviews is handling NULL values. Many candidates get tripped up by their unexpected behavior in comparisons and filtering.

Challenge:

Select all rows where a specific column is either NULL or has a certain value (e.g., NULL or ‘Pending’).

Solution:

SELECT *
FROM Orders
WHERE status IS NULL OR status = 'Pending';

Did you know? Comparing NULL using = never works; always use IS NULL or IS NOT NULL.

6. Pivoting Data with CASE Statements

Data analysts are often asked to reshape data. Pivots allow transformation of row data into columns, and SQL makes this possible even without built-in pivot functions.

Challenge:

Convert a sales data table into a summarized format with monthly sales in separate columns.

Solution:

SELECT product_id,
  SUM(CASE WHEN month = 'Jan' THEN sales ELSE 0 END) AS Jan_Sales,
  SUM(CASE WHEN month = 'Feb' THEN sales ELSE 0 END) AS Feb_Sales,
  SUM(CASE WHEN month = 'Mar' THEN sales ELSE 0 END) AS Mar_Sales
FROM Sales
GROUP BY product_id;

This approach highlights creative thinking and command over conditional aggregations.

7. Self-Joins for Hierarchical Data

Many enterprise datasets contain hierarchical relationships like manager-employee structures. Understanding self-joins is key for navigating such data.

Challenge:

In a table Employees(emp_id, name, manager_id), retrieve each employee along with their manager’s name.

Solution:

SELECT e.name AS employee, m.name AS manager
FROM Employees e
LEFT JOIN Employees m ON e.manager_id = m.emp_id;

Why it’s important: This shows your ability to model relationships and understand aliasing in SQL.

Tips for Interview Success

Aside from solving challenges accurately, keep these tips in mind to make a solid impression:

• Read the question twice: Understanding exact requirements is half the battle.
• Explain your thought process: Interviewers appreciate clear and logical reasoning.
• Be fluent in different SQL dialects: Familiarize yourself with differences in MySQL, PostgreSQL, and SQL Server.
• Test edge cases: Talk about NULLs, duplicates, and performance concerns when presenting your query.

Conclusion

Mastering SQL interview challenges is not just about memorization, but about developing an analytical mindset. As a database analyst, your skill in manipulating and interpreting relational data using SQL will form the backbone of your career.

Whether it’s filtering duplicate records, working with subqueries, or leveraging advanced functions like windowing and CTEs, the practice of solving these real-world challenges will prove instrumental. Approach these problems as not just questions, but opportunities to demonstrate your logic, clarity, and precision—traits of a top-tier analyst.

Ready to face your next database analyst interview? With these SQL challenges and solutions under your belt, your confidence will be backed by practical skills that employers truly value.