Enter into psql terminal: Add a Primary key to users and check the user table. You can a unique constraint and an index added when adding a primary key. Why does adding a primary key also add an index? 👉 It needs the index for speed and to enforce the “no duplicates” rule of primary … Continue reading Rails 8 App: Setup Test DB | Comprehensive Guide 📖 for PostgreSQL , Mysql Indexing – PostgreSQL Heap ⛰ vs Mysql InnoDB B-Tree 🌿