MySQL：多重选择，多重连接？

Question

我有一组多个表（剥离概述）的：

Brand; 
+--------------------+--------------+------+-----+---------+-------+ 
| Field    | Type   | Null | Key | Default | Extra | 
+--------------------+--------------+------+-----+---------+-------+ 
| id     | tinyint(10) | NO | PRI | NULL |  | 
| name    | varchar(255) | NO |  | NULL |  | 
+--------------------+--------------+------+-----+---------+-------+ 

Relations; 
+--------------------+--------------+------+-----+---------+-------+ 
| Field    | Type   | Null | Key | Default | Extra | 
+--------------------+--------------+------+-----+---------+-------+ 
| id1    | tinyint(10) | NO | PRI | NULL |  | 
| id2    | tinyint(10) | NO | PRI | NULL |  | 
+--------------------+--------------+------+-----+---------+-------+ 

Country; 
+--------------------+--------------+------+-----+---------+-------+ 
| Field    | Type   | Null | Key | Default | Extra | 
+--------------------+--------------+------+-----+---------+-------+ 
| id     | tinyint(10) | NO | PRI | NULL |  | 
| name    | varchar(255) | NO |  | NULL |  | 
+--------------------+--------------+------+-----+---------+-------+ 

City; 
+--------------------+--------------+------+-----+---------+-------+ 
| Field    | Type   | Null | Key | Default | Extra | 
+--------------------+--------------+------+-----+---------+-------+ 
| id     | tinyint(10) | NO | PRI | NULL |  | 
| name    | varchar(255) | NO |  | NULL |  | 
+--------------------+--------------+------+-----+---------+-------+ 

每一行都有一个唯一的ID。品牌表中的每一行与国家和城市都有关系。这些表之间的关系存储在关系表中，因此每个品牌行的关系表中有两行。

我试图获得给定品牌ID的品牌名称，国家名称和城市名称。我可以通过单个选择来选择这些关系，但我的目标是在单个查询中执行它（如果可能）。

我能够得到的关系（国家）之一，但我想这个城市还有：

SELECT Brand.name as brand, Country.name as country 
FROM Brand 
LEFT JOIN _relations 
ON Relations.id1 = Brand.id 
INNER JOIN Country 
ON Country.id = Relations.id2 
WHERE Brand.id = '123456'; 

结果：

+-----------+-------------+ 
| brand  | country  | 
+-----------+-------------+ 
| brandname | countryname | 
+-----------+-------------+ 

我的目标是获得：

+-----------+-------------+-------------+ 
| brand  | country  | city  | 
+-----------+-------------+-------------+ 
| brandname | countryname | cityname | 
+-----------+-------------+-------------+ 

任何人都可以帮助我或指出我在正确的方向吗？

Answer 1

加入关系表再次在不同的别名下。

事情是这样的：

SELECT Brand.name as brand, Country.name as country, City.name as city 
FROM Brand 
LEFT JOIN Relations ON Relations.id1 = Brand.id 
INNER JOIN Country ON Country.id = Relations.id2 
LEFT JOIN Relations r2 ON r2.id1 = Brand.id 
LEFT JOIN City ON City.id = r2.id2 
WHERE Brand.id = '123456'; 

Answer 2

基本上你再次加入到关系，然后用它来获得市，所以像

SELECT Brand.name as brand, Country.name as country, City.Name as City 
FROM Brand 
LEFT JOIN _relations relCountry 
ON relCountry.id1 = Brand.id 
INNER JOIN Country 
ON Country.id = relCountry.id2 
LEFT JOIN _relations relCity 
ON relCity.id1 = Brand.id 
INNER JOIN City 
ON City.id = relCity.id2