Both SQL and JSON are used in WurmUnlimited, for those wanting to learn how to work with them a good resource is W3Schools.com as they are free, and teach both of those along with many other programming aspects, mostly web oriented.
Just be aware that WurmUnlimited for the most part uses Java, NOT JavaScript (except the aforementioned JSON of course) which is a completely different thing. Of the 2 they only teach JavaScript there so while it may be interesting it won't help you do too much modding here.