MySQL: Joined table columns without a certain column value - mysql

Question

I have a table that stores file information called files. Each row in the files table can be related to multiple categories and tags.
I have created a table called file_relationships that stores the link between the file and its categories and tags.
Basically what I want to do is filter my results based on certain categories and tags.
So for example I might want to extract all files with the tag number 12 and 15 and files with category number 1 and 2.
However, let's say one of the files had the tag number 12 assigned to it but did not have any category relationships. I'd still want it to be included in the results.
I also want files without any tags and categories assigned to be included. I've acheived this by using fr.relationship IS NULL in my SQLFiddle link below.
I've created a quick mock up of the MySQL code I have been playing with. It's really bad code but hopefully it helps make sense of what I'm trying to achieve.
http://sqlfiddle.com/#!2/931f2/1

Answer 1

I think I have what you are looking for but let me obviously explain what is happening. I am pre-querying (alias PQ) only from the file relationships table an aggregate on each file ID. These aggregates are basically flags of 1 or 0 stating it does or not have something.
The result of the left-join, you want the entry if there are no relationships at all, so your IS NULL is obviously good to go.
Now, your consideration for a file that does not have ANY "TAG" or "CAT" entries. This is where the MAX( IF()) for HasOtherRelation comes in. Through all the entries for a given file ID, all I care about is "are there ANY entries other than cat or tag"... if so, set to 1, otherwise leave 0. Similarly a flag for "HasTagOrCat", so in my where clause I am looking for anything that has an other relation = 1 AND the Has Tag Or Cat flag is zero.
Finally, on to your requirements of meeting your consideration for tag or cat qualifiers but not if the file has other cat or tag entries. Similar MAX( IF()) for those.
select
f.id,
f.file_title
from
files f
LEFT JOIN
( select
fr.file_id,
max( if( fr.relationship IN ('tag','cat'), 1, 0 )) as HasTagOrCat,
max( if( fr.relationship NOT IN ('tag','cat'), 1, 0 )) as HasOtherRelation,
max( if( fr.relationship = 'tag' AND fr.relationship_id IN('12','15'), 1, 0 )) as HasTags,
max( if( fr.relationship = 'cat' AND fr.relationship_id IN('1','2'), 1, 0 )) as HasCats,
max( if( fr.relationship = 'tag' AND fr.relationship_id NOT IN('12','15'), 1, 0 )) as HasOtherTags,
max( if( fr.relationship = 'cat' AND fr.relationship_id NOT IN('1','2'), 1, 0 )) as HasOtherCats
from
file_relationships AS fr
group by
fr.file_id ) PQ
ON f.id = PQ.file_id
where
PQ.file_id IS NULL
OR ( PQ.HasOtherRelation = 1
AND PQ.HasTagOrCat = 0 )
OR ( PQ.HasTags + PQ.HasCats > 0
AND PQ.HasOtherTags + PQ.HasOtherCats = 0 )
So, at the end of the inner pre-query, your results would have the following
File_ID HasTagOrCat HasOtherRelation HasTags HasCats HasOtherTags HasOtherCats
1 1 0 1 1 0 0
2 1 0 1 1 1 1
3 1 0 1 0 0 0
So, your data didn't have any such non tag/cat considerations in the data sample, nor any NULL for no such file entry in relationship table, but the others as summarized above would result in only file 1 & 3 being included in the result set...
They each have AT LEAST a Tag or Cat you were looking for an NO OTHER tag/cat that you did NOT want. For entry 2, yes, it had both a tag and cat you were looking for, but ALSO had other tag/cats that you didnt so that is excluded from result.

Answer 2

replace and with or
--->
(fr.relationship = 'tag' AND fr.relationship_id IN('12','15'))
and (fr.relationship = 'cat' AND fr.relationship_id IN('1', '2'))
you are checking if fr.relationship = 'tag' and fr.relationship = 'cat'
fr.relationship can be 'cat' or fr.relationship can be 'tag' for 1 record/row
can't equal to both values
SELECT f.id,
f.file_title ,fr.relationship
FROM files AS f
LEFT JOIN file_relationships AS fr
ON f.id = fr.file_id
and /*REPLACEMENT as u want null column also */ (
fr.relationship IS NULL
OR (fr.relationship NOT IN ('tag','cat'))
OR (
(fr.relationship = 'tag' AND fr.relationship_id IN('12','15'))
or (fr.relationship = 'cat' AND fr.relationship_id IN('1', '2'))
)
)
GROUP BY f.id
EDIT---
IS THIS WHAT U WANT
http://sqlfiddle.com/#!2/df016d/4
SELECT f.id,
f.file_title ,group_concat(fr.relationship)
FROM files AS f
LEFT JOIN file_relationships AS fr
ON f.id = fr.file_id
and (
fr.relationship IS NULL
OR (fr.relationship NOT IN ('tag','cat'))
OR (
(fr.relationship = 'tag' AND fr.relationship_id IN('12','15'))
or (fr.relationship = 'cat' AND fr.relationship_id IN('1', '2'))
)
)
GROUP BY f.id