midMySQL
Database Index Fundamentals
Updated May 4, 2026
Short answer
Data structures that improve retrieval speed at the cost of write performance.
Deep explanation
Indexes (B-Trees) allow the engine to find rows without a full table scan. They are vital for SELECT performance but slow down INSERTs.
Real-world example
Indexing a 'sku' column to allow instant product lookups.
Common mistakes
- Indexing every column, which bloats storage and hurts performance.
Follow-up questions
- What is a unique index?