I had encountered problem in my update code:
UPDATE kanban_checker_doz SET virtual_doz = (count_doz_chemical_weighing + count_doz_compounding + count_doz_extrusion + count_doz_forming);
it did not work when I have only data in count_doz_chemical_weighing and the other is NULL.
I also tried this code but still the virtual_doz = NULL.
UPDATE kanban_checker_doz SET virtual_doz = ((NULLIF(count_doz_chemical_weighing, 0)) + (NULLIF(count_doz_compounding, 0)) + (NULLIF(count_doz_extrusion, 0)) + (NULLIF(count_doz_forming, 0)));