UPDATE tblitems SET unit = 'hour' WHERE group_id IN (SELECT id FROM tblitems_groups WHERE name = 'Services');

UPDATE tblitems SET unit = 'unit' WHERE group_id IN (SELECT id FROM tblitems_groups WHERE name = 'Products');

UPDATE tblitems SET unit = 'none' WHERE group_id = 0 OR NULLIF(group_id, '') IS NULL;