The correct answer to the question “How many types of constraints are present in SQL Server” is option ©. 6. Types of constraints present in SQL Server are Not Null Constraint, Check constraint, Default Constraint, Unique Constraint, Primary Constraint, and Foreign Constraint. Wish to learn SQL and get certified? Enroll in a good SQL course from Intellipaat. And watch the following video on SQL Interview Questions and Answers from domain experts.