NOT NULL
ConstraintEnsures a column cannot contain NULL values. Every row must have a value for this column.
Syntax
col type NOT NULL
Example
CREATE TABLE products ( id SERIAL PRIMARY KEY, name VARCHAR(100) NOT NULL, price DECIMAL(10,2) NOT NULL );
About SQL NOT NULL
The NOT NULL keyword belongs to the Constraint category of SQL statements. Ensures a column cannot contain NULL values. Every row must have a value for this column. 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 NOT NULL 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 NOT NULL: 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.