SQL Query To Select From Either Or 3 Tables - mysql

Question

Am building a document manager, where a file can belong to many folders(When copied action is being performed from front-end) and a folder can belong to many file likewise, also to keep in mind a file and folder can belong to another folder.With that design i opted for a many to many relationship as that makes a lot of sense. I have three tables folders,files,file_folder where the file_folder is the pivot table.
My Simple DB Schema is defined below :
files:
file_id | name
1 | document.docx
folders:
folder_id | name
1 | root
2 | images
file_folder:
file_id | folder_id | phash
NULL | 2 | 1
1 | NULL | 1
Now the problem is, i have been trying to write a join query that returns a list of both files and folders if they share the same folder,below are the list of queries i have tried but none has been able to return the desired result.
I pretty much want my result this way:
file_id | folder_id | name
1 | NULL | document.docx
NULL | 2 | images
SELECT * FROM
folders dir
JOIN file_folder dir_file
ON dir_file.dir_id = dir.dir_id
JOIN files file
ON dir_file.file_id = file.file_id
WHERE dir_file.dir_id = 1 ORDER BY dir_file.created_at
SELECT * FROM
folders dir,files file
JOIN file_folder dir_file
ON (dir_file.file_id = file.file_id OR dir_file.dir_id = dir.dir_id)
WHERE dir_file.dir_id = 1 ORDER BY dir_file.created_at
I know am just missing something out, that i can't figure out yet. Or maybe am just getting the DB Schema totally wrong. I really don't want to put files and folder on the same table and reference phash(parent folder), this will work but copying a folder with files into another one would just only copy the folder and not the files inside of it, as i will have to duplicate all the sub folders and files to make that happen, which is very bad. I will appreciate if i can get a solution to this
EDITED:
Below works fine for me now!
SELECT * FROM folders dir
LEFT JOIN file_folder dir_file
ON dir_file.dir_id = dir.dir_id
LEFT JOIN files file
ON dir_file.file_id = file.file_id
WHERE dir_file.phash = 1 ORDER BY dir_file.created_at

Answer 1

Due the fact you have not always match between the tables you should use left join
SELECT *
FROM folders dir
LEFT JOIN file_folder dir_file ON dir_file.dir_id = dir.dir_id and dir_file.phash = 1
LEFT JOIN files file ON dir_file.file_id = file.file_id
ORDER BY dir_file.created_at
And in left join move the where condition in On clause (otherwise work as a inner join )