MySQL多连接查询

Question

我有多个表我试图从单个查询中获取数据。我似乎接近一个解决方案，但似乎无法得到我期待的数据结果。是我的表的

实例如下（字段已被截断）：

表C
ID
名称
缩写

表MR（关系表达的关系表C和M一起通过ID）
ID
c.id
m.id

表米
ID

表CNT
ID
c.id

表CMP
ID
cnt.id
活性

我想是从C中的所有字段，来自M的所有字段，其中m.id = c.id，所有活动（活动= 1）来自CMP的id在cnt.id上匹配。

我最近查询（几十个迭代之后）：

SELECT c.id AS id 
    , c.name AS name 
    , c.abbreviation AS abbr 
    , c.active AS active 
    , c.last_modified AS last_modified 
    , c.modified_by AS modified_by 
    , mr.media_id 
    , mr.related_object_table 
    , mr.related_object_id 
    , m.orig_name AS img_name 
    , m.unique_name AS img_slug 
    , m.file_type AS confed_file_type 
    , m.file_size AS file_size 
    , COUNT('cmp.id') AS comps 
FROM confederations AS c 
LEFT JOIN media_relationships AS mr 
ON mr.related_object_id = c.id 
AND mr.related_object_table = 'confederations' 
LEFT JOIN media AS m 
ON m.id = mr.media_id 
INNER JOIN countries AS cnt 
ON cnt.confederations_id = c.id 
INNER JOIN competitions AS cmp 
ON cmp.countries_id = cnt.id 
AND cmp.active = 1; 

我不精通加盟。基本上，我期望的结果是：对于每个联邦（表C），我希望联邦名称，缩写，活动状态（活动），最后修改日期，修改方式;从媒体关系表（表MR），我想要与该联盟相关联的图像ID，以便我可以使用该ID从媒体表（M）中获取联合主图像的图像名称和图像块。

现在我还想要一个给定联盟的比赛总数（表CMP）。国家/地区ID与国家/地区表（国家/地区表）中的主要国家/地区ID关联存储。表CNT中的每个国家都有一个联合身份证。因此，为了获得每个联盟的比赛总数，我试图通过表CNT中的CONFEDERATIONS_ID将所有国家都纳入其各自的联盟中，然后在联盟中我想从表CMP中选择所有比赛，并且匹配来自国家编号组的COUNTRIES_ID对于给定的邦联。 （在这一点上，我认为我很困惑自己如何得到我想要的）

不知何故，我得到了正确的比赛数，但我得到重复的联合会作为结果。比如我我得到一些类似的（假设我有2,1和3场分别比赛3个不同联合会）：

Competitions 1 : name 1 | abbreviation 1 | image 1 | total competitions = 2; 
Competitions 1 : name 1 | abbreviation 1 | image 1 | total competitions = 1; 
Competitions 1 : name 1 | abbreviation 1 | image 1 | total competitions = 3 

我到底做错了什么？

Answer 1

经过反复试验，其实我对我自己解决了这个。我回来后我的答案，看看德感的答案，但它是写比我不同我认为它非常接近我结束了：

SELECT 
    cnf.id AS confed_id, cnf.name AS confed_name, cnf.abbreviation AS 
    confed_abbr, cnf.active AS confed_active, cnf.modified_by AS 
    confed_mod_by, cnf.last_modified AS confed_last_mod, 
    COUNT(cnt.id) AS total_countries, 
    COUNT(cmp.id) AS total_comps, 
    mr.media_id, mr.related_object_table, mr.related_object_id, 
    mr.primary_img, 
    m.orig_name AS img_name, m.unique_name AS img_slug, m.file_type AS file_type 
FROM confederations AS cnf 
LEFT JOIN media_relationships AS mr 
ON mr.related_object_id = cnf.id AND mr.related_object_table = 'confederations' 
LEFT JOIN media AS m 
ON m.id = mr.media_id 
LEFT JOIN countries AS cnt 
ON cnt.confederations_id = cnf.id AND cnt.active = 1 
LEFT JOIN competitions AS cmp 
ON cmp.countries_id = cnt.id AND cmp.active = 1 
GROUP BY cnf.id 

所以farthis似乎给我结果我可以使用。我不确定，如果我选择的所有连接的左连接实际上给了我我需要的一切（它会成为SEEMS），并且在表格变大时是否会省略/添加记录。如果任何人都可以在我的查询中指出一个问题，并且我选择使用左连接而不是像Degan那样使用左连接和内连接，那会很有帮助。

Answer 2

聚合时，你需要分组。

也许这是接近你在找什么：

SELECT c.id AS id 
    , c.name AS name 
    , c.abbreviation AS abbr 
    , m.orig_name AS img_name 
    , SUM('cmp.id') AS comps 
FROM confederations AS c 
LEFT JOIN media_relationships AS mr 
    ON mr.related_object_id = c.id 
    AND mr.related_object_table = 'confederations' 
LEFT JOIN media AS m 
    ON m.id = mr.media_id 
INNER JOIN countries AS cnt 
    ON cnt.confederations_id = c.id 
INNER JOIN competitions AS cmp 
    ON cmp.countries_id = cnt.id 
    AND cmp.active = 1 
GROUP BY c.id AS id 
     , c.name AS name 
     , c.abbreviation AS abbr 
     , m.orig_name AS img_name