Data

primary key

A primary key is the column in a database table whose value uniquely identifies each row — the one stable handle by which you can always point at exactly one record. Like a student ID or an order number, it answers the question 'which exact row do you mean?' with no ambiguity.

Two rules make it special: it must be unique (no two rows can share the same value) and it can never be empty. The database itself enforces this, so you can't accidentally end up with two customers wearing ID 42. Often it's a plain auto-incrementing number the database hands out for you, one per new row.

Why bother? Because names and emails change, and people share them, but a primary key is the one thing you can rely on to mean the same row forever. It's also what other tables point at when they need to reference this row — the anchor a foreign key grabs onto.

CREATE TABLE users (
  id    INTEGER PRIMARY KEY,
  email TEXT NOT NULL
);

Mark a column PRIMARY KEY and the database guarantees every row's id is present and unique.

A table has exactly one primary key, but that key can span several columns together when no single column is unique on its own.

Also called

pkid columnunique identifier