FOREIGN KEY

Constraint

Establishes a relationship between tables by referencing a primary key in another table.

Syntax

FOREIGN KEY (col) REFERENCES table(col)

Example

CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  user_id INTEGER,
  FOREIGN KEY (user_id) REFERENCES users(id)
    ON DELETE CASCADE
);

About SQL FOREIGN KEY

The FOREIGN KEY keyword belongs to the Constraint category of SQL statements. Establishes a relationship between tables by referencing a primary key in another table. Understanding this command is essential for any developer working with relational databases like PostgreSQL, MySQL, SQLite, or SQL Server.

SQL (Structured Query Language) is the standard language for managing and querying relational databases. The FOREIGN KEY statement is supported across all major database systems, though specific syntax may vary slightly between PostgreSQL, MySQL, MariaDB, Oracle, SQL Server, and SQLite. Always consult your database's documentation for vendor-specific features and limitations.

Best practices for using FOREIGN KEY: always test queries on a development database before running them in production, use parameterized queries to prevent SQL injection, and leverage EXPLAIN to understand query performance. For complex queries, consider using CTEs (Common Table Expressions) to improve readability and maintainability.

Related SQL Keywords

PRIMARY KEYON DELETE