---
title: "Primary Key — Database Glossary | Xata"
description: "A constraint guaranteeing that one or more columns uniquely identify each row and contain no NULLs. A table can have at most one primary key. Automatica..."
source: "https://xata.io/glossary/primary-key"
---

# Primary Key

Core Database

A constraint guaranteeing that one or more columns uniquely identify each row and contain no NULLs. A table can have at most one primary key. Automatically creates a unique B-tree index.

Related terms

[Constraint](/glossary/constraint)[Unique Constraint](/glossary/unique-constraint)[B-tree](/glossary/b-tree)

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