Use this calculation:
If ( Patterncount ( List ( Projects::Status ) ; "Open" ) ; "Open Project Exists" )
If you have filemaker 11, Put a portal to projects on your customer layout. Add this portal filter to the portal setup for it:
Projects::Status = "Open"
This portal can now be used to list all the open projects for this customer.
Option 3: (A way to do the same if you do not have FileMaker 11)
Define a calculation field in Customer, constOpen, select "text" as the calculation return type and enter "Open" (in quotes) as the sole calculation term. Then make a new table occurrence of Projects and name it OpenProjects. Relate it to customers like this:
Customers::CustomerID = OpenProjects::CustomerID AND
Customers::constOpen = OpenProjects::Status
With this relationship, a portal to OpenProjects can be used like Option to to list all open projects. And (unlike option 2), a calculation field with: Count ( OpenProjects::CustomerID ) will return the number of open projects.
There are also other approaches possible.
Patterncount did the trick. Amazing.
Thank you so much.