SQLMedium
How do you find the second highest salary in SQL?
Use a subquery that takes the MAX salary below the overall MAX, or use DENSE_RANK() and pick rank 2, which also handles ties and generalises to the Nth highest.
Junior 路 Mid-level 路 SQL
Backend Developer 路 Intern to senior
Backend Developer Interview Questions and Answers
Backend interviews test how you store, process and serve data reliably: language fundamentals, SQL and indexing, concurrency, API design and how systems behave under load.
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131 questions
- SQLMedium
How do you find and delete duplicate rows in SQL?
Find duplicates with GROUP BY and HAVING COUNT(*) > 1, then delete them by numbering rows within each duplicate group with ROW_NUMBER() and removing every row after the first.
Junior 路 Mid-level 路 SQL - SQLMedium
What is database normalization and what are the normal forms?
Normalization is organising tables to reduce redundancy and update anomalies: 1NF means atomic values, 2NF removes partial dependencies on part of a composite key, and 3NF removes dependencies between non-key columns.
Junior 路 Mid-level 路 Database - C#Medium
What is the difference between an abstract class and an interface in C#?
An abstract class can hold state, constructors and partial implementation but a class can inherit only one, while an interface defines a contract that a class can implement many of.
Junior 路 Mid-level 路 Object-Oriented Programming - C#Medium
What is boxing and unboxing in C# and why does it affect performance?
Boxing converts a value type to object by allocating it on the heap, and unboxing converts it back; both add allocations and casts, so avoid them in hot code paths.
Junior 路 Mid-level 路 Performance - C#Medium
What is LINQ in C# and what is deferred execution?
LINQ (Language Integrated Query) lets you query collections, databases and XML with a consistent syntax, and deferred execution means a query does not run when you define it but when you enumerate the results.
Junior 路 Mid-level 路 Functions & Scope - JavaMedium
What is the difference between an abstract class and an interface in Java?
An abstract class can have instance fields, constructors and a mix of implemented and abstract methods but supports only single inheritance, while an interface defines a contract that a class can implement multiple times and, since Java 8, can include default methods.
Junior 路 Mid-level 路 Object-Oriented Programming - JavaMedium
What is the difference between ArrayList and LinkedList in Java?
ArrayList is backed by a resizable array with O(1) index access and O(n) insertion in the middle, while LinkedList is a doubly linked list with O(n) index access and O(1) insertion once you hold the node; in practice ArrayList is faster for most workloads.
Junior 路 Mid-level 路 Data Structures - JavaMedium
What is the difference between checked and unchecked exceptions in Java?
Checked exceptions (subclasses of Exception other than RuntimeException) must be caught or declared with throws, while unchecked exceptions (RuntimeException and Error) do not have to be handled and usually signal programming bugs.
Junior 路 Mid-level 路 Programming Fundamentals - JavaMedium
What are the main features of Java 8: lambdas, streams and Optional?
Java 8 introduced lambda expressions, functional interfaces, the Stream API for declarative collection processing, Optional to represent missing values, default methods in interfaces, method references and the java.time date and time API.
Junior 路 Mid-level 路 Functions & Scope - PythonMedium
Why should you not use a mutable default argument in Python?
Default argument values are evaluated once when the function is defined, so a default list or dictionary is shared between every call that does not pass its own, causing data to leak between calls.
Junior 路 Mid-level 路 Functions & Scope - PythonMedium
What is the difference between a shallow copy and a deep copy in Python?
A shallow copy creates a new container but reuses the same nested objects, while a deep copy recursively copies everything so the new object is fully independent.
Junior 路 Mid-level 路 Data Structures - PythonMedium
What is the difference between @staticmethod and @classmethod in Python?
A classmethod receives the class as its first argument (cls) and can create or configure instances, while a staticmethod receives no automatic argument and is just a function placed inside the class namespace.
Junior 路 Mid-level 路 Object-Oriented Programming - System DesignMedium
What is a load balancer and what are the common load balancing algorithms?
A load balancer distributes incoming requests across several servers to improve capacity and availability, using algorithms such as round robin, least connections or consistent hashing.
Junior 路 Mid-level 路 System Design - GitMedium
What is the difference between git merge and git rebase?
Both integrate changes from one branch into another: merge keeps both histories and joins them with a merge commit, while rebase rewrites your commits so they appear on top of the target branch, giving a linear history.
Junior 路 Mid-level 路 Git - GitMedium
How do you resolve a merge conflict in Git?
Open the conflicted files, decide what the final code should be between the conflict markers, remove the markers, run the tests, then stage the files and continue the merge or rebase.
Junior 路 Mid-level 路 Git - DockerMedium
How do you write a good Dockerfile? What are multi-stage builds?
Use a small, pinned base image, order instructions so dependencies are cached before source code, use multi-stage builds to leave build tools out of the final image, run as a non-root user and keep secrets out of the image.
Junior 路 Mid-level 路 DevOps - Software TestingMedium
What is mocking in testing and when should you use it?
Mocking replaces a real dependency with a controllable fake so a test can run in isolation and check how the code interacts with it; use it for slow, non-deterministic or external dependencies, not for everything.
Junior 路 Mid-level 路 Testing - JavaScriptMediumCoding
How do you flatten a nested array in JavaScript without using flat()?
Recursively walk the array: when an element is an array, flatten it and append the result; otherwise append the element. An iterative version uses an explicit stack to avoid recursion limits.
Junior 路 Mid-level 路 Coding Problems - BehavioralMediumBehavioral
How do you answer "Tell me about a difficult project you worked on"?
Choose a real project with a technical or organisational challenge, explain your specific role and decisions with the STAR method, and finish with the result and what you learned.
Junior 路 Mid-level 路 Behavioral Interviews