Importance of Data Integrity and Constraints:

Data Integrity ensures accuracy, consistency, reliability of data - prevents invalid entries, maintains business rules. Without integrity, database contains garbage, queries wrong, application fails.

Constraints enforce integrity declaratively:

• Primary Key (Entity Integrity): Uniquely identifies row, prevents duplicates/NULL. Example: Student rollno PK ensures no duplicate student.

• Foreign Key (Referential Integrity): Ensures reference exists or NULL, prevents orphan. Example: Enroll(s_id) FK references Student, cannot enroll non-existent student, cascade delete maintains.

• NOT NULL, UNIQUE, CHECK, DEFAULT, Domain constraints: Enforce valid ranges, e.g., CHECK (age>0), salary >0.

• Benefits: Centralized enforcement, not reliant on app code, prevents anomalies, automatic validation, easier maintenance. Example without PK, duplicate inserts cause inconsistency.