sorting on field - how to set it up?
In stock module, I have 'inventory control' -> 'products'; when switched to list view I can see list as on pisture attached. Problem I have is that I can sort the list using for example 'product type' column (marked green), but cannot sort using 'quantity on hand' nor 'forecasted quantity'. View name used for the list is 'product.template.product.tree'; column 'quantity on hand' and 'forecasted quantity' are inherited from other, 'product.template.stock.tree.inherit'.
How to make fields marked in red on picture, labeled as:
to be sortable?