MySQL group_concat +子查询或substring_index

Question

我有两张桌子：

- tb_shops
shop_id PK
shop_name

- tb_products

product_id PL
product_name
shop_id FK

我需要列出类似的内容：

shop_name | product01,product02,product03,product04
shop_name2 | product05,product06,product07,prodcut08

但这些产品每个商店需要限制4个。

我试过这些问题：

使用子查询进行拳击

select SQL_NO_CACHE a.shop_id,
        a.shop_name,
        count(b.product_id) as ptotal,
        (select group_concat(_b.product_name separator ',') from tb_shops _a left join tb_products _b using(shop_id) where _a.shop_id=a.shop_id group by _a.shop_id limit 4) as products 
from tb_shops a 
left join tb_products b on a.shop_id=b.shop_id 
group by a.shop_id
order by a.shop_name asc

第二个是substring_index

select SQL_NO_CACHE a.shop_id,
        a.shop_name,
        count(distinct b.product_id) as ptotal,
        substring_index(group_concat(distinct c.product_name separator ','),',',4) as products 
from tb_shops a 
left join tb_products b on a.shop_id=b.shop_id 
left join tb_products c on a.shop_id=c.shop_id 
group by a.shop_id
order by a.shop_name asc

哪些更好？或者有人知道更好的解决方案？