SQL vs NoSQL, Indexing, and Why Database Design Dominates Backend Interviews

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A developer-focused dialogue on DEV Community uses a mentor-nephew format to explain why database knowledge is heavily tested in backend engineering interviews. The core argument is that unlike application code, a flawed database schema is extremely costly to fix once live data populates it, making data handling a key measure of senior engineering skill. The piece contrasts SQL databases like PostgreSQL with NoSQL options like MongoDB, emphasizing that neither is universally superior and that the right choice depends on the specific data requirements of each use case. For example, financial transactions demand SQL's ACID guarantees, while high-volume chat logs or event streams are better suited to NoSQL's horizontal scalability. The article advises developers to select databases based on the problem at hand rather than personal preference, noting that most serious production systems deliberately use both types for different data needs.

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