7 SQL Coding Questions for Data Analysts and Data Scientists

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.