Data Constraints

Data constraints in SQL are rules applied to columns or tables to enforce data integrity and consistency. They include primary key, foreign key, unique, check, and not null constraints. These constraints define limitations on the data that can be inserted, updated, or deleted in a database, ensuring that the data meets specific criteria and maintains relationships between tables. By implementing data constraints, database designers can prevent invalid data entry, maintain referential integrity, and enforce business rules directly at the database level.