Hi
See what is constraint ? Constraint is basically used to impose some limitation in Data base to get the uniformity in Data Base.
Commonly used constraints
1. Primary key - Which uniquely identifies row in a table.
2. Foreign Key - Which is used to refers to the other table.
3. Check - To have a validation checks on input/output
4. Not Null - It will not allow null values.
5. Unique. - Repetition of the values are not allowed.
To clear your basics in RDBMS go through some sql server interview questions at http://www.wiziq.com/online-class/292863-sql-server-interview-questions
Thanks
Regards
Kolla Sanjeeva Rao
OCP Oracle.
