#Database

Discuss techniques for SQL query optimization, including the use of indexing, utilizing `EXPLAIN`, avoiding `SELECT *`, denormalization, and analyzing slow query logs.

Design the APIs, data entities, relationships, and database schema for an Amazon feature called 'Notify Me' that informs users about sales. Consider how the feature interacts with the existing system.

What is indexing in databases? Explain how it improves query performance and what happens internally to achieve this efficiency.

Design an AdClick Aggregator Service with a focus on multiple design approaches, including Lambda vs Kappa architecture, database schema design, entity relationships, indexing, and the choice between SQL and NoSQL databases. Justify your choices with real use cases and address concerns around scaling, fault tolerance, and observability.

Design a database schema for a system that manages entities with multiple stages, evaluations, and results over time, supporting repeated attempts and outcomes at different stages. Discuss your design choices and any trade-offs involved.