In the Database Diagram, when I dragged and dropped a parent table over, nothing happened, no linked child tables appeared, no
entity relationship. We have to set this manually to get it to work and that is counter productive. Now when I dragged over a parent table and it automatically pulled in 2 additional child tables and linked them, but there were many other tables that it didn't link, why is that.
The reason why the tables didn't automatically link is because the table structure does not have any Foreign key constraint in them. If the table script have a Foreign key constraint then the tables will be automatically loaded when you dragged one table into the Database Diagram. The relational link will be a solid line and you will not be able to remove the link.
If the tables are dragged into the diagram and are not automatically link, then you manually link them. These relational links will be a dash line and you can right click and remove them. These link are only for the database diagram and are not coming from the original table structure. Therefore, after manually linking these tables, if you drag just one table into the diagram, it will not load all the other tables. You have to drag all the tables involved or save the diagram and open it up in order to show all the table relationship.