Here's a link to get you started on Gaps and Islands.
The SQL of Gaps and Islands in Sequences [/url]
It's a pretty advanced topic though so some of the links provided earlier may serve you better, even though they have little to do with this topic. All of Itzik Ben-Gan's books are great help to beginners trying their hands on advanced topics.
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St