Does Ignition have the means to support "Api" calls to the local SQL Database?
A web API call, yes. In either direction (via the WebDev module for external requests to Ignition). Other technologies, not so much.
How simple/hard is this to implement? Can you recommend some reading I could do on this matter?
Also, what do you mean by "other technologies, not so much"?
There are all kinds of posts on this forum for implementing various types of web APIs with WebDev. The WebDev module's own documentation is kinda thin, and IA basically tells you that you are on your own. But fundamentally, it is jython that unpacks the parameters for a particular named query, runs the query, and converts the output into json for the reply to the caller.
As for "other technologies", I meant any non-web-based protocol. Which you can do, but it will have to be done at a socket level, with your own protocol-level message encoder and decoders, all wrapped in a bunch of guards for dealing with jython thread life cycles. Probably easier to write a java add-on module for such things.
Thanks "pturmel" you always have great information, and I appreciate your help.