SQL: query with complex subqueries - mysql

Question

I have the following tables in my game's database:
rankedUp (image_id, user_id, created_at)
globalRank (image_id, rank )
matchups (user_id, image_id1, image_id2)
All image_ids in globalRank table are assigned a rank which is a float from 0 to 1
Assuming I have the current logged in user's "user_id" value, I'm looking for a query that will return a pair of image ids (imageid1, imageid2) such that:
imageid1 has lower rank than imageid2 but is also the next highest rank less than imageid2
matchups table doesn't have (userid,imageid1,imageid2) or (userid,imageid2,imageid1)
rankedup table doesn't have (userid,imageid1) or if it does, the createdat column is older than X hours
What I have so far for requirement 1 is this:
SELECT lowerImages.image_id AS lower_image, higherImages.image_id AS higher_image
FROM global_rank AS lowerImages, global_rank AS higherImages
WHERE lowerImages.rank < higherImages.rank
AND lowerImages.image_id = (
SELECT image_id
FROM (
SELECT image_id
FROM global_rank
WHERE rank < higherImages.rank
ORDER BY rank DESC
LIMIT 1 , 1
) AS tmp
)
but it doesnt work because I can't reference higherImages.rank in the subquery.
Does anyone know how I could satisfy all of those requirements in one query?
Thanks for your help
EDIT:
I now have this query but I don't know about the efficiency and I need to test it for correctness:
SELECT lowerImages.image_id AS lower_image,
max(higherImages.image_id) AS higher_image
FROM global_rank AS lowerImages, global_rank AS higherImages
WHERE lowerImages.rank < higherImages.rank
AND 1 NOT IN (select 1 from ranked_up where
lowerImages.image_id = ranked_up.image_id
AND ranked_up.user_id = $user_id
AND ranked_up.created_at > DATE_SUB(NOW(), INTERVAL 1 DAY))
AND 1 NOT IN (
SELECT 1 from matchups where user_id = $userId
AND lower_image_id = lowerImages.image_id
AND higher_image_id = higherImages.image_id
UNION
SELECT 1 from matchups where user_id = $user_id
AND lower_image_id = higherImages.image_id
AND higher_image_id = lowerImages.image_id
)
GROUP BY 1
the "not in" statements I'm using are all indexed so they should run fast. The efficiency problem I have is the group by and selection of the global_rank tables
This question is a revision of Pretty Complex SQL Query, which should no longer be answered.

Answer 1

select
(
select image_id, rank from
rankedup inner join globalRank
on rankedup.image_id = globalRank .image_id
where user_id = XXX
limit 1, 1
) as highest,
(
select image_id, rank from
rankedup inner join globalRank
on rankedup.image_id = globalRank .image_id
where user_id = XXX
limit 2, 1
) as secondhighest
I normally use SQL Server, but this i think is the translation for mysql :)

Answer 2

This should do the trick:
SELECT lowerImages.*, higherImages.*
FROM globalrank AS lowerImages, globalrank AS higherImages
WHERE lowerImages.rank < higherImages.rank
AND lowerImages.image_id = (
SELECT image_id
FROM (
SELECT image_id
FROM globalrank
WHERE rank < higherImages.rank
ORDER BY rank DESC
LIMIT 1,1
) AS tmp
)
AND NOT EXISTS (
SELECT * FROM matchups
WHERE user_id = $user_id
AND ((image_id1 = lowerImages.image_id AND image_id2 = higherImages.image_id)
OR (image_id2 = lowerImages.image_id AND image_id1 = higherImages.image_id))
)
AND higherImages.image_id NOT IN (
SELECT image_id FROM rankedup
WHERE created_at < DATE_ADD(NOW(), INTERVAL 1 DAY)
AND USER_ID <> $user_id
)
ORDER BY higherImages.rank
I'm assuming the PKs of matchups and rankedup include all columns in those tables. This would allow the second 2 sub-queries to utilize the PK indexes. You would probably want an ordered index on globalrank.rank to speed up the first sub-query.