Remarks to Previous Answer
Azure Data Factory is a whole new product and oversized, I think it's not appropriate for the relatively small size of what I want to do.
Answer
To get the SQL data into the Stream Analytics you have to save it in a Blob Storage (a simple WebApp is enough) and then it can be used to inside the Stream Analytics to enrich the data which is coming from the IoT Hub (e.g. appending a location to an object which is known to the front end but has no location in the front end due to data separation concerns).
In the Azure Blob Storage a snapshot from the current state of the SQL database is stored - this is okay for me because neither the amount nor the location of my objects changes very often, so updates to the Blob Storage are very infrequent.
In the Azure Stream Analytics a Blob Storage can be used to append information to a model, so here the model ids can be matched and a location can be appended, then the modified model can be saved again to a blob storage for a later data analysis.