SQL Constraints

SQL constraints are rules applied to database tables to ensure data accuracy and integrity. They specify what kind of data can be stored, prevent errors, and maintain consistency. Examples include "NOT NULL" (value must be provided), "UNIQUE" (no duplicates), "PRIMARY KEY" (a unique identifier for each row), "FOREIGN KEY" (links data between tables), and "CHECK" (limits data to certain conditions). Constraints help prevent invalid entries, enforce relationships, and keep the database reliable and well-structured.