Viewed
Explanation
Google
Gemini 2.5 Pro
VS
OpenAI
GPT-5 mini
Explain Database Indexing to a Junior Developer
You are a senior software engineer mentoring a junior developer who has been writing SQL queries for about six months but has never thought about performance optimization. They just encountered their first slow query on a table with two million rows and asked you: "What is database indexing, and how do I know when to use it?"
Write a clear, teaching-oriented explanation that covers the following:
1. What a database index is and an intuitive analogy that makes the concept click.
2. How an index speeds up query performance, including a brief mention of the underlying data structure (such as B-trees) explained in accessible terms.
3. The trade-offs of indexing — when indexes help and when they can actually hurt performance.
4. Practical guidance on deciding which columns to index, with at least two concrete examples using realistic table and column names.
5. A brief note on composite indexes and when they matter.
Your explanation should be conversational yet precise, appropriate for someone who understands basic SQL but has no computer science background in data structures. Avoid unnecessary jargon, but do not oversimplify to the point of inaccuracy.
