mySQL使用JOIN计数出现次数

mySQL使用JOIN计数出现次数,mysql,join,count,one-to-many,Mysql,Join,Count,One To Many,我的事件系统有一个标记系统,我想创建一个“标记云” 我有活动,可以有多个“类别” 以下是表格结构: **Event_Categories** (Stores Tags / Categories) | id | name | +-----------------+ + 1 | sport | + 2 | charity | + 3 | other_tag | **Events_Categories** (Linking Table) | event_id

我的事件系统有一个标记系统,我想创建一个“标记云”

我有活动,可以有多个“类别”

以下是表格结构:

**Event_Categories** (Stores Tags / Categories)
| id  | name      |
+-----------------+
+ 1   | sport     |
+ 2   | charity   |
+ 3   | other_tag |


**Events_Categories** (Linking Table)
| event_id  | event_category_id |
+-------------------------------+
+    1      |       1           |   
+    2      |       2           |   
+    3      |       1           |   
+    3      |       2           |   
总结:

Event ID 1 -> Sport
Event ID 2 -> Charity
Event ID 3 -> Sport, Charity
我想退回以下物品:

| tag_name  | occurrences |
+-----------+-------------+
|  sport    |     2       |
|  society  |     2       |
other_标记-未实际返回,因为它已出现0次

谢谢!:)

这将起作用:

SELECT c.name AS tag_name, COUNT(ec.event_id) AS occurrences 
FROM Event_Categories c 
INNER JOIN Events_Categories ec ON c.id = ec.event_category_id 
GROUP BY c.id
如果要包括发生次数为0的类别,请将
内部联接更改为
左联接
,这将起作用:

SELECT c.name AS tag_name, COUNT(ec.event_id) AS occurrences 
FROM Event_Categories c 
INNER JOIN Events_Categories ec ON c.id = ec.event_category_id 
GROUP BY c.id

如果要包含发生次数为0的类别,请将
内部联接更改为
左联接

SELECT e.name,
COUNT(1)
FROM Event_Categories e INNER JOIN
Events_Categories_Linking ec ON e.id = ec.event_category_id
GROUP BY e.name

像这样的怎么样

SELECT e.name,
COUNT(1)
FROM Event_Categories e INNER JOIN
Events_Categories_Linking ec ON e.id = ec.event_category_id
GROUP BY e.name

谢谢,但是即使没有,它也会返回事件数=1?此外,计数似乎不正确?谢谢,但是即使没有,也会返回次数=1?而且计数似乎不正确?