Question

所以，我有一些名为文件和文件夹的表格，其中包含ID和常用关系：file.folder_id = folder.id

此外，字段忽略可以忽略某些文件/文件夹。

我正在尝试获取相应文件夹中的文件夹列表和文件计数。我的第一种方法工作正常，但错过了空文件夹：

SELECT folders.id, folders.name, count(files.id) kount
FROM folders, files

WHERE folders.site_id=111
AND files.ignored=0
AND folders.ignored=0 
AND files.site_id=111
AND files.folder_id=folders.id

GROUP BY folders.name 
ORDER BY folders.name

所以我寻找LEFT JOIN

SELECT folders.id, folders.name, count(files.id) kount
FROM folders 


LEFT JOIN files 
ON files.folder_id=folders.id

WHERE folders.site_id=111
AND folders.ignored=0
AND files.ignored=0
AND files.site_id=111


GROUP BY folders.name 
ORDER BY folders.name

但是再次 - 缺少空文件夹。我做错了什么？

Answer 1

您需要将连接表的条件直接放入left join

SELECT folders.id, folders.name, count(files.id) kount
FROM folders 
LEFT JOIN files ON files.folder_id=folders.id
               AND files.ignored=0
               AND files.site_id=111
WHERE folders.site_id=111
AND folders.ignored=0
GROUP BY folders.name 
ORDER BY folders.name

Answer 2

试试这个。

SELECT folders.id, folders.name, count(files.id) kount
FROM folders 


LEFT JOIN files 
ON files.folder_id=folders.id
AND files.ignored=0
AND files.site_id=111

WHERE folders.site_id=111
AND folders.ignored=0



GROUP BY folders.name 
ORDER BY folders.name

SQL JOIN - 将所有左行分组

2 个答案: