Primary Key
A column (or combination of columns) that uniquely identifies each row in a database table. Must be unique and not null.
What is Primary Key?
A column (or combination of columns) that uniquely identifies each row in a database table. Must be unique and not null.
Primary Key is a foundational concept that sits in the Database Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Primary Key" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn Primary Key in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the Primary Key lessonSee also
Related glossary terms you might want to look up next.
Foreign Key
A column in one table that references the primary key of another table, enforcing referential integrity between related tables.
Index
A data structure that speeds up database lookups. Like the index at the back of a book that lets you jump to the right page instead of reading every page.
SQL
Structured Query Language for managing relational databases. Tables, rows, columns, and powerful joins to query related data.