group twice in one query - sql

Question

I use below code but doesn't return what I expect,
the table relationship,
each gallery is include multiple media and each media is include multiple media_user_action.
I want to count each gallery how many media_user_action and order by this count
rows: [
{
"id": 1
},
{
"id": 2
}
]
and this query will return duplicate gallery rows something like
rows: [
{
"id": 1
},
{
"id": 1
},
{
"id": 2
}
...
]
I think because in the LEFT JOIN subquery select media_user_action rows only group by media_id,
need to group by gallery_id also ?
SELECT
g.*
FROM gallery g
LEFT JOIN gallery_media gm ON gm.gallery_id = g.id
LEFT JOIN (
SELECT
media_id,
COUNT(*) as mua_count
FROM media_user_action
WHERE type = 0
GROUP BY media_id
) mua ON mua.media_id = gm.media_id
ORDER BY g.id desc NULLS LAST OFFSET $1 LIMIT $2
table
gallery
id |
1 |
2 |
gallery_media
id | gallery_id fk gallery.id | media_id fk media.id
1 | 1 | 1
2 | 1 | 2
3 | 2 | 3
....
media_user_action
id | media_id fk media.id | user_id | type
1 | 1 | 1 | 0
2 | 1 | 2 | 0
3 | 3 | 1 | 0
...
media
id |
1 |
2 |
3 |
UPDATE
There's more other table I need to select, this is a part in a function like this https://jsfiddle.net/g8wtqqqa/1/ when user input option then build query.
So I correct my question I need to find a way if user want to count media_user_action order by it, I wanna know how to put these in a subquery possible not change any other code
Base on below #trincot answer I update code, only add media_count on top change a little bit and put those in sub query. is what I want,
now they are group by gallery.id, but sort media_count desc and asc are same result not working I can't find why?
SELECT
g.*,
row_to_json(gi.*) as gallery_information,
row_to_json(gl.*) as gallery_limit,
media_count
FROM gallery g
LEFT JOIN gallery_information gi ON gi.gallery_id = g.id
LEFT JOIN gallery_limit gl ON gl.gallery_id = g.id
LEFT JOIN "user" u ON u.id = g.create_by_user_id
LEFT JOIN category_gallery cg ON cg.gallery_id = g.id
LEFT JOIN category c ON c.id = cg.category_id
LEFT JOIN (
SELECT
gm.gallery_id,
COUNT(DISTINCT mua.media_id) media_count
FROM gallery_media gm
INNER JOIN media_user_action mua
ON mua.media_id = gm.media_id AND mua.type = 0
GROUP BY gm.gallery_id
) gm ON gm.gallery_id = g.id
ORDER BY gm.media_count asc NULLS LAST OFFSET $1 LIMIT $2

Answer 1

The join with gallery_media table is multiplying your results. The count and grouping should happen after you have made that join.
You could achieve that like this:
SELECT g.id,
COUNT(DISTINCT mua.media_id)
FROM gallery g
LEFT JOIN gallery_media gm
ON gm.gallery_id = g.id
LEFT JOIN media_user_action mua
ON mua.media_id = gm.id AND type = 0
GROUP BY g.id
ORDER BY 2 DESC
If you need the other informations as well, you could use the above (in simplified form) as a sub-query, which you join with anything else that you need, but will not multiply the number of rows:
SELECT g.*
row_to_json(gi.*) as gallery_information,
row_to_json(gl.*) as gallery_limit,
media_count
FROM gallery g
LEFT JOIN (
SELECT gm.gallery_id,
COUNT(DISTINCT mua.media_id) media_count
FROM gallery_media gm
INNER JOIN media_user_action mua
ON mua.media_id = gm.id AND type = 0
GROUP BY gm.gallery_id
) gm
ON gm.gallery_id = g.id
LEFT JOIN gallery_information gi ON gi.gallery_id = g.id
LEFT JOIN gallery_limit gl ON gl.gallery_id = g.id
ORDER BY media_count DESC NULLS LAST
OFFSET $1
LIMIT $2
The above assumes that gallery_id is unique in the tables gallery_information and gallery_limit.

Answer 2

You're grouping by media_id to get a count, but since one gallery can have many gallery_media, you still end up with multiple rows for one gallery. You can either sum the mua_count from your subselect:
SELECT g.*, sum(mua_count)
FROM gallery g
LEFT JOIN gallery_media gm ON gm.gallery_id = g.id
LEFT JOIN (
SELECT media_id,
COUNT(*) as mua_count
FROM media_user_action
WHERE type = 0
GROUP BY media_id
) mua ON mua.media_id = gm.media_id
GROUP BY g.id
ORDER BY g.id desc NULLS LAST;
id | sum
----+-----
2 | 1
1 | 2
Or you can just JOIN all the way through and group once on g.id:
SELECT g.id, count(*)
FROM gallery g
JOIN gallery_media gm ON gm.gallery_id = g.id
JOIN media_user_action mua ON mua.media_id = gm.id
GROUP BY g.id
ORDER BY count DESC;
id | count
----+-------
1 | 2
2 | 1

Answer 3

If you only want to show data from table gallery (with select g.*) then why do you join the other tables? Outer joins either join one ore more records to each main record (depending on how many matches are found in the outer-joined table), so no surprise you get duplicates (in your case because gallery ID 1 has two matches in gallery_media).