Great questions here and actually something that comes up during talks on how to make some of these things more understandable.
The empty brackets,
 are just what you mentioned, an empty array.
In the first formula you posted, there was sort of an error in that nothing would be returned, but the formula was written properly and would return a list if the data it was trying to referenced was reachable. So it’s been difficult to figure out when Coda should show an error and when Coda should show that it’s a validly written formula, but not returning results.
For the other questions around
thisRow and what are these things actually referencing, there are a few visual indicators that can help.
In your “Events” table and the “Employee” column, it is a lookup to your “Employees” table. What you are choosing in the dropdown there is actually the full row of the employee and not just the name. So that
Events.Employee column, in the first row for “Jill” is actually the full dataset of “Name:Jill, Department: R&D”.
So if you create a new column and just use dot notation, you don’t need a lookup at all to find the department. You can simply reference the “Employee” column which is really a row from the “Employees” table, and then reference the “Name” column from that table.
This will give you the Name and
Employee.Department will give you department.
The visual indicator of what is a full row reference is the blue capsule around the text. If you hover over that, you’ll see the info from the original table.