How can I create a record in invoices at the moment I create a visit.

I've a table customers, visits and invoices.

Now the invoices are linked to customers an created manualy. In the future I want to create a invoice record at the moment I've enterd a date in the visit table where the invoice is linked to the visit record.

It means that I first want to link the actual created invoice record to the visits and secondly the script to create the invoice record.

The problem I found that against SQL I don't have a tool to run a query to see what I'm doing and also I can't see the fields that creates the link.

This evening 14/01/19 I'll join the Webinair. If possible I like to hear the answer there.