select 
    workorder.*, tag.*, 
    concat(user_info.first_name, ' ', user_info.last_name) as assigned_to_user_str,
    suppliers.company_name as assigned_to_supplier_str,
    tag_categories.name as category_str, 
    locations.name as location_str
    
    from tag, locations, tag_categories, workorder  
    left join user_info on workorder.assigned_to_user = user_info.id 
    left join suppliers on workorder.assigned_to_supplier = suppliers.supplier_id 
    WHERE workorder.tag_id = tag.tag_id and 
    workorder.location = locations.id and 
    workorder.prev_maint=1 and
    tag_categories.id = workorder.category