TO enforce the integrity of the data in the columns, CONSTRAINTS are very useful. In this regard SQL Server provides various mechanims in enforcing such integrity: PRIMARY KEY Constraints FOREIGN KEY Constraints UNIQUE Constraints CHECK Constraints DEFAULT Definitions Allowing Null Values Further steps are required in the database design to identify valid values for a column and to decide how to enforce the integrity of the data in the column. Data integrity falls into the following categories: Entity...(<a href="http://sqlserver-qa.net/blogs/t-sql/archive/2010/10/01/9628.aspx">read more</a>)<img src="http://sqlserver-qa.net/aggbug.aspx?PostID=9628" width="1" height="1">