PRIMARY KEY
ConstraintUniquely identifies each row in a table. Cannot contain NULL values. One per table.
Syntax
col type PRIMARY KEY | CONSTRAINT name PRIMARY KEY (cols)
Example
CREATE TABLE users ( id SERIAL PRIMARY KEY, email VARCHAR(255) NOT NULL );
About SQL PRIMARY KEY
The PRIMARY KEY keyword belongs to the Constraint category of SQL statements. Uniquely identifies each row in a table. Cannot contain NULL values. One per 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 PRIMARY 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 PRIMARY 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.