SQL proficiency is a critical skill for data analysts and data scientists, and SQL coding interviews are a common way for employers to assess a candidate’s database querying skills. In this article, we’ll explore 12 SQL interview coding questions frequently encountered in data-related job interviews. Each question is accompanied by a detailed explanation and a code example to help you prepare effectively for your next SQL interview.
Question 1: Retrieve Unique Values
Problem:
Retrieve unique values from a column in a table.
Solution:
SELECT DISTINCT column_name FROM your_table;
Question 2: Filtering Rows
Problem:
Filter rows based on a specific condition.
Solution:
SELECT * FROM your_table WHERE condition;
Question 3: Aggregation and Grouping
Problem:
Calculate the total count and average of a column, grouped by another column.
Solution:
SELECT category, COUNT(*) AS total_count, AVG(price) AS average_price
FROM your_table
GROUP BY category;
Question 4: Sorting and Limiting Rows
Problem:
Sort rows in descending order and limit the result to the top N rows.
Solution:
SELECT * FROM your_table ORDER BY column_name DESC LIMIT N;
Question 5: Joining Tables
Problem:
Combine data from two tables using INNER JOIN.
Solution:
SELECT t1.column1, t1.column2, t2.column3
FROM table1 t1
INNER JOIN table2 t2 ON t1.common_column = t2.common_column;
Question 6: Subqueries
Problem:
Use a subquery to filter results based on another query’s output.
Solution:
SELECT column1, column2
FROM your_table
WHERE column3 IN (SELECT column3 FROM another_table WHERE condition);
Question 7: Window Functions
Problem:
Calculate the running total using a window function.
Solution:
SELECT date, revenue, SUM(revenue) OVER (ORDER BY date) AS running_total
FROM your_table;
Conclusion:
Mastering these 7 SQL interview coding questions will significantly enhance your readiness for data-related job interviews. As you practice these queries and understand the underlying principles, you’ll be well-equipped to tackle a variety of SQL challenges. Remember to not only provide correct answers but also communicate your thought process effectively during interviews.
