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System Design Basics for Backend Developers · Lesson

Indexing and Query Optimization

Understand how database indexes work, when to use them, and how to optimize queries for fast reads without crippling writes.

Why Indexes Matter

Without an index, finding a row means scanning every row — a full table scan. As tables grow into millions of rows, this becomes painfully slow.

An index is a separate data structure that lets the database jump straight to matching rows.

The B-Tree Index

Most relational indexes use a B-tree: a balanced tree that keeps keys sorted. Lookups, range scans, and ordering all become logarithmic instead of linear.

  • Fast equality lookups (WHERE id = 5)
  • Fast range queries (WHERE age > 30)
  • Supports ORDER BY without re-sorting

All lessons in this course

  1. SQL vs. NoSQL Databases
  2. Sharding and Data Replication
  3. Data Consistency Models
  4. Indexing and Query Optimization
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