How to make Location column populated with data?

[cduduc]

I have PS 1.6.1.19.

I have added:

$this->fields_list['location'] = array(
            'title' => $this->l('Location'),
            'width' => 30
        );

For the Location column to be visible in the Products list but the column is empty with no values.

How exactly the syntax for $this->_join should be? I know I need to add that query as well in order for the column to get values. Or not?

Thank you in advance!