从 4 个带有连接和 IN 的表中选择

Question

我有 5 张桌子。
先给products点赞：

id | country_ids | category_ids | users_ids  
1  | 1,4,6       |  4,5,6,70    | 5,6,9  
2  | 5,6,3       |  4,8,2,11    | 1,5,8  

第二个countries点赞：

c_id | c_name  
1  | Åland Islands  
2  | Antarctica  
...  

第三个categories点赞：

cat_id | cat_name  
2  | Small  
4  | Large    
...  

第四桌users赞：

u_id | u_name  
1  | David  
2  | Mary    
...  

第五张表review（表结构不重要，只计算id）。

和sql

SELECT a.*, COUNT(b.comm_id) AS comm_count, c.*, d.*, e.* FROM 产品作为 LEFT JOIN cmets AS b ON b.comm_prod_id = a.id AND b.comm_published = 1 LEFT JOIN countries AS c ON c.c_id IN (a.country_ids) LEFT JOIN 类别 AS d ON d.c_id IN (a.category_ids) LEFT JOIN users AS e ON e.c_id IN (a.users_ids) /*发布地点 = 1*/ 按 ID 分组 ORDER BY id DESC 限制 0, 5

但是这个查询只返回连接表的第一个值。

我怎样才能得到这样的行

1 | Åland Islands, Equador, Russia | Small, tiny, large, ... | Anna, John, Linda  

PS！还是我需要为每个表创建表关系？什么很不喜欢。

Answer 1

使用 GROUP_CONCAT() 函数：

SELECT 
    a.id, 
    GROUP_CONCAT(DISTINCT c_name) AS country_names, 
    GROUP_CONCAT(DISTINCT cat_name) AS cat_names, 
    GROUP_CONCAT(DISTINCT u_name) AS user_names, 
    COUNT(DISTINCT b.comm_id) AS comm_count
FROM products AS a
LEFT JOIN comments AS b ON b.comm_prod_id = a.id AND b.comm_published = 1
LEFT JOIN countries AS c ON c.c_id IN (a.country_ids)
LEFT JOIN categories AS d ON d.c_id IN (a.category_ids)
LEFT JOIN users AS e ON e.c_id IN (a.users_ids)
/*WHERE published = 1*/
GROUP BY id
ORDER BY id DESC
LIMIT 0, 5

更新： 哦，伙计，您的表格中有一个逗号分隔的列表。很烂。
阅读规范化并创建具有结构 product_cmets(product_id, comment_id), product_countries(product_id, country_id) 的关系表，并将每个关系存储在单独的行中。

示例数据：

product_countries  
product_id, country_id  
1, 1
1, 4
1, 6
2, 5
2, 6
2, 3