define column sortable wordpress code example
Example: make posts_custom_column sortable
add_filter( 'manage_edit-cake_sortable_columns', 'my_sortable_cake_column' );
function my_sortable_cake_column( $columns ) {
$columns['slices'] = 'slice';
//To make a column 'un-sortable' remove it from the array
//unset($columns['date']);
return $columns;
}