In his first article for Simple-Talk, Joe Celko demystifies the use of Constraints, and points out that they are an intrinsic part of SQL and are a great way of ensuring that a business rule is done one way, one place, one time.  Read more...

I am modifying a table and I need to add a column that must be defined as being unique. I see that SQL Server allows you to define a UNIQUE constraint on a column but I also see that you can create a unique index on a column. Which one should I use?  Read more...

Over the years, I have witnessed many developers being confused about when to use data-manipulation language (DML) triggers vs. when to use constraints.  Read more...

Some time ago, I loaded a large set of data into one my tables. To speed up the load, I disabled the FOREIGN KEY and CHECK constraints on the table and then re-enabled them after the load was complete. I am now finding that some of the loaded data was referentially invalid. What happened?  Read more...

By using cascading referential integrity constraints, you can define the actions that SQL Server 2005 takes when a user tries to delete or update a key to which existing foreign keys point.  Read more...