Hash vs Inverted vs Composite vs Covering Index | Database Indexing Part 2 | Day 5

0:00 Intro: what we'll cover 0:48 Quick recap: the B-Tree 1:40 Hash index: how it works 5:06 Hash index limits & real-world use 7:59 Inverted index & full-text search 13:44 Composite index 17:10 Column order & the leftmost prefix rule 18:57 Covering index 21:19 Choosing the right index 22:06 Interview questions 24:02 Final mental model & what's next 🔔 Subscribe to Hello Backend for daily backend interview prep. #DatabaseIndexing #SystemDesign #BackendInterview #SQL #SoftwareEngineering Tags database indexing, hash index, inverted index, composite index, covering index, database index types, leftmost prefix rule, full text search, elasticsearch, postgresql index, gin index, system design interview, backend interview preparation, sde 2 interview, sql performance, query optimization Which database index should you use? In Day 5 of Backend Interview Preparation, we go beyond the B-Tree and learn the four index types that come up most in system design interviews: hash indexes, inverted indexes, composite indexes, and covering indexes. For each index, we start with a real query problem, see how the index solves it, and talk about what it costs. You'll learn: ✅ How a hash index works (buckets, pointers, collisions) and why it can't do range queries ✅ Why LIKE '%word%' can't use a B-Tree, and how an inverted index powers full-text search (Elasticsearch, PostgreSQL GIN) ✅ How a composite index handles filter + sort in one scan, and the leftmost prefix rule ✅ When a covering index (INCLUDE) is worth it, and when it isn't ✅ How to answer the most common indexing interview questions Perfect for SDE-1 engineers preparing for SDE-2 / SDE-3 backend and system design interviews at Google, Amazon, Microsoft, Meta, Uber and more.