How do you create a normalized database schema from a given set of requirements? Describe the process. Write an SQL query to find all customers who have made more than three purchases in the last month. Explain the difference between LEFT JOIN and INNER JOIN. What are indexes in SQL? How do they improve query performance, and when should you avoid using them? How would you handle database transactions in SQL? Provide an example of transaction control. Describe how you would implement a queue using two stacks. Given an array of integers, write a function to return the indices of two numbers such that they add up to a specific target. Explain the difference between depth-first search (DFS) and breadth-first search (BFS) in graph traversal. What is a binary search tree? How do you insert and find elements in it?

How do you improve the performance of a Node.js application? Explain the concept of clustering in Node.js. How do you handle memory leaks in Node.js applications? What are callbacks, promises, and async/await? How do you handle errors in asynchronous code? What is the event loop, and how does it work?