SQL Interview Preparation: Top Patterns and Practice Questions

Why SQL Interviews Matter

SQL is tested in interviews for backend engineers, data analysts, data scientists, and even some frontend roles. Companies like Google, Amazon, Meta, and Flipkart all include SQL rounds.

The good news: SQL interview questions follow predictable patterns. Master the patterns, and you can handle most questions.

Pattern 1: Aggregation + GROUP BY

The most common pattern. You're asked to find totals, averages, counts, or max/min values grouped by a category.

-- Find average GPA per course
SELECT c.title, AVG(s.gpa) AS avg_gpa
FROM courses c
JOIN enrollments e ON c.id = e.course_id
JOIN students s ON e.student_id = s.id
GROUP BY c.id, c.title
ORDER BY avg_gpa DESC;

Key tip: Remember that every non-aggregated column in SELECT must appear in GROUP BY.

Pattern 2: Top-N per Group

Find the top N items within each group. This is where window functions shine:

WITH ranked AS (
  SELECT
    name,
    department,
    salary,
    ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) AS rn
  FROM employees
)
SELECT name, department, salary
FROM ranked
WHERE rn <= 3;

This finds the top 3 highest-paid employees in each department.

Pattern 3: Self-Joins and Date Comparisons

Finding consecutive events, comparing rows, or detecting sequences:

-- Find employees who earned more than their manager
SELECT e.name AS employee, m.name AS manager
FROM employees e
JOIN employees m ON e.manager_id = m.id
WHERE e.salary > m.salary;

Self-joins are trickier to visualize but follow the same JOIN logic — the table is just joined with itself.

Practice Strategy

1. Master the basics first — SELECT, WHERE, GROUP BY, HAVING, ORDER BY
2. Learn JOINs deeply — INNER, LEFT, RIGHT, self-joins
3. Practice window functions — ROW_NUMBER, RANK, LAG/LEAD
4. Write CTEs — Common Table Expressions make complex queries readable
5. Time yourself — Interview questions should take 10-15 minutes each

Use Ira SQL Pro's playground to practice with real data. The AI assistant can review your queries and suggest optimizations — exactly the kind of feedback you'd get in a real interview.