我有一个数据库查询

$extras = DB::select(

        'SELECT p.*
        FROM products p 
        WHERE required_product IS NULL 
        UNION ALL
SELECT p.* 
FROM products p, orders o 
WHERE p.required_product = o.product_id 
AND o.user_id =' .  $user->id .  'UNION ALL
SELECT p.* , "onlyOnce" product_type
FROM products p, orders o, only_once on 
WHERE p.required_product = o.product_id
AND p.id = on.product_id 
AND p.id NOT IN (SELECT product_id FROM orders WHERE o.product_id = p.id and o.user_id ='.$user->id.')'
);

以下是我的表格结构：
产品表：http://prntscr.com/k6jdv7
订单表： product_id,user_id 用户表： id,name,last_server,timestamps