Constraints are rules that help maintain data and referential integrity.
Data integrity means that the data is valid in the database.
Referential integrity means that the relationships are valid between tables.
Contraints prevent incorrect data from entering into the database.
SQL Server supports different types of constraints.
Click each link for more details.
| Constraint | Description | |
|---|---|---|
| Primary Key | A column that uniquely identifies each row in a table | |
| Foreign Key | A column in one table that uniquely identifies a row in another table | |
| NOT NULL | Specifies that the values in a column cannot be NULL | |
| CHECK | Specifies that the values in a column must satisfy a condition | |
| UNIQUE | Specifies that the values in a column must be unique | |
| DEFAULT | Specifies a default value for a column if no value is specified |
