Say I have a table with the following layout:
Id Int PRIMARY KEY IDENTITY
DateFrom datetime NOT NULL
DateTo datetime NOT NULL
UserId Int
UserId is a foreign key to a users table, and well obviously there’s more data which is irrelevant to this question.
What I want to do, is to make sure that per User, there can not be any overlapping “periods”, that is, say we have a row of data for User 1, from the 15th of May 2009 to the 18th of May 2009, then there cannot be any other rows in the database that contains any of those dates (15-18th of May 2009, both dates included).
How would I go about this in the best way? My initial thinking would be to use triggers, but I’m not exactly sure how and/or if there’s a better way of doing some more “custom” data validation like this?
My friend I beleive you are spot on. Triggers are designed for this exact reason, to implement Business Rules.
The Books Online documentation has a few examples that will help to get you started.
http://msdn.microsoft.com/en-us/library/ms189799.aspx