I would like to learn if agile software development methods/principles/patterns are valid to SQL programming as well. If yes, where would be a good place to start learning about that? Are there any articles or books targeting agile development in SQL context?
Yes. There is a whole web site devoted to it: Agile Data
I'm using it now for a brand new project.
Also see: Should you design the database before the application code is written?. My answer there doesn't capture what I do now: 2 week sprints, good enough for that sprint. As per the Agile Data site
I've been doing Agile development for more than four years, including my SQL Server projects, and I really like it. I think it is important to understand why and when Agile is useful, from the perspective of the whole system, and general purpose Agile-related books such as the following fit the bill: " Agile Principles, Patterns, and Practices in C#", " Patterns of Enterprise Application Architecture".
The following two books are focused on database development, as you asked, but I would read the general purpose ones first: "Agile database techniques", "Refactoring databases"