Join three Tables to create an Access Granted List - mysql

Question

I have three tables I would like to join to pull off a MySQL Query that will check to see if a user has access to download photo. Each photo has its own access rights which can be one of the following.
Level one - any user can download the photo.
Level two - only users who have access can download the photo.
Table 1: FILES
FILE_ID is AUTO_INCREMENT
USER_ID is the identifier of the user that owns the file.
FILE_NAME is just the name of the photo.
FILE_ACCESS is the access rights to the 2 levels noted above.
FILE_ID | USER_ID | FILE_NAME | FILE_ACCESS
1 | 3 | 1279141923.jpg | 1
2 | 3 | 1279141925.jpg | 1
3 | 3 | 1279141927.jpg | 2
4 | 4 | 1279141929.jpg | 1
5 | 4 | 1279141931.jpg | 2
6 | 3 | 1279141933.jpg | 2
Table 2: USERS
USER_ID is AUTO_INCREMENT
USER_NAME is just the name of the file owner.
USER_ID | USER_NAME
1 | jack
2 | jill
3 | john
4 | mike
Table 3: ACCESS
ACCESS_ID is AUTO_INCREMENT
USER_ID is the identifier of the user that owns the file.
ALLOW_ID is the identifier of the user that has access all the file uploaded by user.
ACCESS_ID | USER_ID | ALLOW_ID
1 | 3 | 1
2 | 3 | 4
User Jack has access to download photos 1279141923.jpg, 1279141925.jpg and 1279141927.jpg that John has uploaded while Jill only has access to 1279141923.jpg and 1279141925.jpg
Jack gets access to all three as files 1 and 2 have access level one while he also gets access to download file 3 seeing that John has given him full access to all files uploaded by John.
SELECT a.file_name, b.user_name FROM files AS a
JOIN users AS b ON a.user_id = b.user_id
WHERE a.file_access = '1'
This MySQL Query gives me the following when Jill is signed in.
1279141923.jpg, john (owner name)
1279141925.jpg, john
1279141929.jpg, mike
I am now looking to introduce the ACCESS table into this Query, so that if Jill is signed in she is displayed with the same results as above will if Jack was signed he would get the following results.
1279141923.jpg, john (owner name)
1279141925.jpg, john
1279141927.jpg, john
1279141929.jpg, mike
1279141933.jpg, john
I hope I explain this right, as I sure need help with the last portion. I am not quite sure how to add this to the current Query. I can do it using multiple queries - but I prefer if possible would like to leave it as one.

Answer 1

SELECT DISTINCT(F.id), F.filename
FROM files F, ACCESS A
WHERE F.flie_access=1
OR (F.user_id=2)
OR (F.user_id = A.user_id AND A.allow_id=2);
So, you can access the file if it is:
level 1 (ie public)
or you are the owner
or you have a matching access entry in the 'ACCESS' table.
You seem to have granted access to ALL a users files to another user, you might want to consider a "USER_ACCESS" and a "FILE_ACCESS" table to grant other people access to either all your files or just a specfific file.

Answer 2

Tim, here is the modified query...
SELECT F.file_name, U.user_name
FROM files AS F
INNER JOIN users AS U USING (user_id)
LEFT OUTER JOIN access AS A USING (user_id)
WHERE (A.allow_id = 1 AND F.file_access IN (1, 2))
OR (A.allow_id IS NULL AND F.file_access = 1)
ORDER BY F.file_id
With multi-table JOINs, you have to be careful because the memory footprint of such join operations are significantly large, particularly if the tables are large -- which I am assuming they are (or will be as soon as your app picks up lot of user traffic). Sometimes, separating the query is not such a bad thing.
Just my 2 cents... HTH
Ashwin