how to sort in vue table 2 for scope column

Hello ,

I have the column "full name" composed by two values : first_name, last_name. it works very well except for the order , when I click the header column 'Full name' it returns no order . !

                <span slot="fullName" slot-scope="{row}">
                 {{row.last_name}} {{row.first_name}}
                </span>

 columns: ['status', 'fullName', 'activity', 'job_title', 'abbreviation', 'email', 'actions'],
                rows: [],
                options: {
                    sortable: ['fullName'],
                    filterByColumn: false,
                    perPage: 5,
                    texts: {
                        filter: "",
                        filterBy: 'Filter {column}',
                        count: ''
                    },
                    pagination: {chunk: 10, dropdown: false},
                    filterable: ['name','email'],
                    headings: {
                        status: 'Status',
                        fullname: 'Full name',
                        activity: 'Activity',
                        job_title: 'Job Title',
                        users: 'Members',
                        abbreviation: 'Abrv',
                        email: 'Email',
                        actions: "Actions"
                    }