multiple AND on same joined table coulmnn - mysql

Question

I have three table images, image_tags and tags. image table contains images info, tags contains tags info and image_tags contains relationship between images and tags, relationship is many to many. I want to filter images based on multiple tags with AND condition (not IN).
I have tried :
SELECT images.* FROM images
LEFT JOIN image_tags ON image_tags.image_id = images.id
LEFT JOIN tags tag_0 ON image_tags.tag_id = tag_0.id
LEFT JOIN tags tag_1 ON image_tags.tag_id = tag_1.id
WHERE tag_0.tag = "tagme"
AND tag_1.tag = "excellent"
AND images.filesize > 0
GROUP BY images.id
ORDER BY images.posted DESC LIMIT 0, 40
AND
SELECT images.* FROM images
LEFT JOIN image_tags ON image_tags.image_id = images.id
LEFT JOIN tags ON image_tags.tag_id = tags.id
WHERE tags.tag = "tagme"
AND tags.tag = "excellent"
AND images.filesize > 0
GROUP BY images.id
ORDER BY images.posted DESC LIMIT 0, 40
But nothing worked it is always returning zero results though they exist.

Answer 1

Your first query, even though it uses a LEFT join, requires hits in tags on both "tagme" and "excellent", because the condition is in the where clause. Move the condition into the ON clause, like this:
SELECT images.* FROM images
LEFT JOIN image_tags ON image_tags.image_id = images.id
LEFT JOIN tags tag_0 ON image_tags.tag_id = tag_0.id AND tag_0.tag = 'tagme'
LEFT JOIN tags tag_1 ON image_tags.tag_id = tag_1.id AND tag_1.tag = 'excellent'
WHERE images.filesize > 0
GROUP BY images.id
ORDER BY images.posted DESC LIMIT 0, 40
Your second query is way off - it has an impossible condition:
WHERE tags.tag = "tagme"
AND tags.tag = "excellent"
tags.tag can not be both "tagme" and "excellent".

Answer 2

None of your attempt is correct enough, though the first one is closer to the correct one. To filter the tags the way you are trying to filter them, you'll need to join to image_tags twice and join both instances of tags to separate instances of image_tags. And it seems like you want to do inner joins rather than outer joins. Here:
SELECT i.*
FROM images i
INNER JOIN image_tags it0 ON it0.image_id = i.id
INNER JOIN tags t0 ON t0.id = it0.tag_id
INNER JOIN image_tags it1 ON it1.image_id = i.id
INNER JOIN tags t1 ON t1.id = it1.tag_id
WHERE i.filesize > 0
AND t0.tag = 'tagme'
AND t1.tag = 'excellent'
ORDER BY i.posted DESC
LIMIT 0, 40
There's another way you could do the same. Try the following:
SELECT i.*
FROM images i
INNER JOIN image_tags it ON it.image_id = i.id
INNER JOIN tags t ON t.id = it.tag_id
WHERE i.filesize > 0
AND t.tag IN ('tagme', 'excellent')
GROUP BY i.id
HAVING COUNT(DISTINCT i.tag) = 2
ORDER BY i.posted DESC
LIMIT 0, 40
The t.tag IN ('tagme', 'excellent') condition limits allowed tags to the specified list and HAVING COUNT(DISTINCT i.tag) = 2 makes sure the image has got all of them.