Top Django, SQL, and AWS Interview Questions and Answers

If you are preparing for Python/Django backend interviews, then you’ll not only face questions on Django itself but also on SQL, APIs, caching, and cloud (AWS). Therefore, in this blog, I’ve compiled some of the most frequently asked questions along with clear and concise answers. However, these examples will help you understand the concepts better and prepare more effectively for your next interview.

My advice is to prepare more questions in SQL because, for Django developers, it is often difficult to learn SQL due to relying heavily on the ORM. Therefore, practicing SQL separately will strengthen your backend fundamentals and give you more confidence in interviews.

1. What is the Longest Substring Problem?

The longest substring problem usually refers to finding the longest substring without repeating characters.

Example: For "abcabcbb"the answer is "abc“.
Approach: Use a sliding window + a hashmap/set.
Time Complexity: O(n).

def longest_substring(s):
    seen = set()
    left = 0
    start = 0
    max_len = 0
    for right in range(len(s)):
        while s[right] in seen:   # shrink window if duplicate found
            seen.remove(s[left])
            left += 1
        seen.add(s[right])
        if (right - left + 1) > max_len:
            max_len = right - left + 1
            start = left  # track start index of longest substring
    
    return s[start:start + max_len]
# Example
print(longest_substring("abcabcbb"))  # Output: "abc"

2. What are the Types of Indexing in Databases?

A database technique that speeds up query performance by creating data pointers:

Primary Index – automatically created on the primary key.
Unique Index – ensures uniqueness (e.g., email).
Clustered Index – rearranges the physical order of rows (only one per table).
Non-Clustered Index – stores pointers to actual rows (multiple allowed).
Composite Index – index on multiple columns.
Full-text Index – used for searching text.

3. How Do I Write the Longest SQL Query?

This is a trick question — instead of “long queries,” interviewers expect optimized queries.

Use CTEs (WITH clause) to break down large queries.
Avoid unnecessary joins.
Always optimize with proper indexing.

4. How Do You Make Fast APIs in Django Rest Framework (DRF)?

Ways to optimize DRF APIs:

Use select_related() and prefetch_related() to avoid N+1 queries.
Serialize only required fields.
Add pagination.
Implement caching (Redis/Memcached).
Use async views (if supported).

5. Can an Anonymous User Store Cart Items?

An anonymous user’s cart items can be stored using sessions or cookies. The cart data (like product IDs and quantities) is kept in the session or browser storage until the user logs in. Once they log in, the session/cart data is merged into the user’s permanent cart stored in the database.

6. How Do You Store Frequently Accessed Product Images Efficiently?

Store images in static files or cloud storage (S3, GCP).
Use the Django cache framework (Redis/Memcached) to cache image paths.
Add CDN (CloudFront, Cloudflare) for faster delivery.
Enable browser caching with proper HTTP headers.

7. What is Middleware in Django?

Middleware is a layer between the request and the response. These are predefined in django: Authentication, Session, CSRF, and Security headers.

Custom Middleware Example:

class SimpleMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        print("Before View:", request.path)
        response = self.get_response(request)
        print("After View:", response.status_code)
        return response

8. How Do You Optimize Django ORM Queries?

Use select_related() for ForeignKey joins.
Use prefetch_related() for ManyToMany relations.
Use .only() / .defer() to fetch only the needed fields.
Use bulk_create/bulk_update.
Cache results using Redis.
Monitor queries with django-debug-toolbar.

9. How Do You Write Raw SQL Queries in Django?

Two main ways of user raw or user cursor connection:

Using .raw() → returns model objects.

users = UserProfile.objects.raw("SELECT * FROM user WHERE active = %s", [True])

Using connection.cursor() → returns tuples.

from django.db import connection
with connection.cursor() as cursor:
    cursor.execute("SELECT id, name FROM user WHERE active = %s", [True])
    rows = cursor.fetchall()

10. What AWS Services Have You Used?

Compute: EC2, Lambda, ECS/EKS.
Storage: S3, EBS, EFS.
Database: RDS, DynamoDB, Aurora, ElastiCache.
Networking: VPC, Route53, CloudFront, API Gateway.

11. What is Load Balancing in AWS?

Load balancing distributes incoming traffic across multiple servers. AWS provides Elastic Load Balancer (ELB):

Application Load Balancer (ALB) → Layer 7 (HTTP/HTTPS).
Network Load Balancer (NLB) → Layer 4 (TCP/UDP).
Gateway Load Balancer (GLB) → For firewalls/security appliances.
Classic Load Balancer (CLB) → Legacy.

12. What are the Types of JOIN Queries in SQL?

In SQL, JOINs combine rows from two or more tables based on related columns. They allow you to fetch meaningful data by linking multiple tables together. Different types of JOINs define how records from one table are matched with records from another.

INNER JOIN → Only matching rows.
LEFT JOIN → All rows from left + matches from right.
RIGHT JOIN → All rows from right + matches from left.
FULL OUTER JOIN → All rows from both.
CROSS JOIN → Cartesian product.
SELF JOIN → Table joined with itself.

13. How Does LEFT JOIN Work?

LEFT JOIN returns all rows from the left table and matching rows from the right. Non-matching → NULL.

Example:

SELECT e.name, d.dept_name
FROM Employees e
LEFT JOIN Departments d
ON e.dept_id = d.id;

14. How Do You Implement Push Notifications in Django?

Mobile (FCM/APNs): Use Firebase Cloud Messaging. Store device tokens in DB, send via pyfcm.
Web Push: Use django-webpush or pywebpush with Service Workers.
Third Party: OneSignal, AWS SNS.

15. What is Redis, and How Did You Use It?

Redis serves as a high-performance caching and message broker.
Use cases in Django:

Caching queries.
Session storage.
Celery broker for background tasks.
Pub/Sub for real-time notifications.

Example (Django cache):

from django.core.cache import cache
def get_product(pid):
    key = f"product:{pid}"
    product = cache.get(key)
    if not product:
        product = Product.objects.get(id=pid)
        cache.set(key, product, 3600)
    return product

Preparing for Python/Django backend interviews requires a balance of theory and practical knowledge. While Django and its ORM simplify a lot of work, interviewers often test your understanding of SQL, system design, caching, and cloud services like AWS. Therefore, practice coding problems, revisit core SQL queries, and explore concepts like load balancing, middleware, and caching. With consistent preparation, you’ll not only perform well in interviews but also become a more confident backend developer. See my previous Python Interview question.