Windows – Searching inside XML files from Windows Explorer

This would obviously be suboptimal, but have you tried copying the .SQL files to .TXT files?

I don't mean simply rename, since you are presumably using the SQL files as SQL files somewhere. But if you have the space, make copies and rename those to .SQL.TXT or so. If your SQL files change frequently, schedule a task to re-create the copies.

This would be worthwhile as an experiment -- if Windows Desktop Search can successfully index a .SQL.TXT file, there's something about the .SQL extension that it's failing on. If it can't, something about the file's format is confusing it.

According to MSDN, the nothing character is []. So press F3 and enter ext:[].