Hello everyone and thank you in advance for your help.
My problem boils down to "how do I sum the durations in a linked table?" ...
Here is the detail of the structure of my database where the problem arises: I have a "projects" table to which a "tasks" table is attached (type 1 to n relation). The "tasks" table is itself linked to a "sessions" table where the duration of each session is recorded. In the "tasks" table, I manage to have the sum of the durations for each task by cumulating the durations of the sessions. But how do you go to a higher level, in the "projects" table?
Indeed, in this table, if I add a "sum" column, I only get an unusable number ...
Voil, hoping to have been clear enough.