Answer
Constraints declare rules that table data must satisfy. • Common constraints include NOT NULL, CHECK, UNIQUE, PRIMARY KEY, and FOREIGN KEY. • They centralize integrity rules inside the database. • Constraint enforcement can reject invalid INSERT or UPDATE statements.
💡 SQL Example
CREATE TABLE products (product_id integer PRIMARY KEY, price numeric CHECK (price >= 0));
Result
CREATE TABLE
⚡ Quick Revision
Constraints make the database enforce data rules.