Constraints and Keys

🔐 Constraints and Keys

SQL Server supports various constraints to enforce data integrity:

| Constraint     | Description                                      |
|----------------|--------------------------------------------------|
| PRIMARY KEY    | Ensures unique, non-null values per row          |
| FOREIGN KEY    | Links a column to another table's PK             |
| UNIQUE         | Ensures unique values, allows NULLs              |
| CHECK          | Enforces a condition on column values            |
| NOT NULL       | Prevents null entries in a column                |
| DEFAULT        | Provides a default value if none is provided     |