Default Value/SQL query to pull all active assignment hours for an employee

Summary:

I am trying to make a new flexfield that displays Total Working Hours for an employee across all active assignments. This is to help easily identify total working hours in one space, rather than looking at each assignment individually.

I would like to create a read-only descriptive flexfield. When creating the DFF, under the Initial Default Section, am selecting Default Type: SQL. Can anyone provide assistance with generating the Default Value /SQL query? I am getting stuck on how to make it specific to the employee displayed.