Select rows when all all ids of its children records matches

Maybe this:
select p.id, p.name
from posts p,
     posts_tags pt,
     tags t
where t.id in (1, 2, 3)
  and t.id = pt.tag_id
  and pt.post_id = p.id;

On 09/12/2018 10:23 AM, Arup Rakshit wrote:

I have a table posts(id, name), posts_tags(post_id, tag_id) and tags (id,
name) ... I want to get all posts which has tag id 1, 2 and 3 for example.
How should I do this? I tried ALL, but it didn’t work.

Those tag ids comes from UI by users, so I am looking for generic approach.

Thanks,

Arup Rakshit
ar@zeit.io <mailto:ar@zeit.io>

--
Angular momentum makes the world go 'round.

IN is OR, I want the AND logic. Select posts which has tag 1, 2 and 3 ( tag ids )

Thanks,

Arup Rakshit
ar@zeit.io

On Wednesday, September 12, 2018, Arup Rakshit <ar@zeit.io> wrote:

IN is OR, I want the AND logic. Select posts which has tag 1, 2 and 3 (
tag ids )

Build arrays and then use the “contains” operator.

David J.

Can you show me the SQL construction? Do I need to use `WITH`?

Thanks,

Arup Rakshit
ar@zeit.io

On 12 Sep 2018, at 17:44, Arup Rakshit <ar@zeit.io> wrote:

Can you show me the SQL construction? Do I need to use `WITH`?

An option is to create a bit-wise OR and SUM the grouped results. If the result of these 3 bits is 7, than the post matches all three tags.

select p.id, p.name
from post p
join post_tag pt on (pt.post = p.id)
join tag t on (t.id = pt.tag)
where t.id in (1, 2, 3)
group by
case t.id
when 1 then 1
when 2 then 2
when 3 then 4
else 0
end
having sum(case t.id
when 1 then 1
when 2 then 2
when 3 then 4
else 0
end) = 7;

I used ints here for the bitwise OR, a bitstring would probably be neater.

Another approach is to aggregate the set of matching tags into an array using array_agg(). I think that's what David means. You could then check the length of the array to see if you have all 3 (or 4 or 5 or 9000).

On 12-Sep-2018, at 9:13 PM, David G. Johnston <david.g.johnston@gmail.com> wrote:

On Wednesday, September 12, 2018, Arup Rakshit <ar@zeit.io> wrote:
IN is OR, I want the AND logic. Select posts which has tag 1, 2 and 3 ( tag ids )

Build arrays and then use the “contains” operator.

David J.

Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.

I tried :

WITH posts_tags_cte AS (
SELECT post_id, array_agg(tag_id) as tags
FROM posts_tags
WHERE tag_id in (1, 2)
GROUP BY post_id
)
SELECT posts.id FROM posts_tags_cte JOIN posts ON posts.id = posts_tags_cte.post_id
WHERE posts_tags_cte.tags @> array[1, 2]::int8[]

But it gives me all the posts.

Thanks,

Arup Rakshit
ar@zeit.io

On 09/12/2018 10:08 AM, Arup Rakshit wrote:

I tried :

WITH posts_tags_cte AS (
        SELECT post_id, array_agg(tag_id) as tags
        FROM posts_tags
        WHERE tag_id in (1, 2)
        GROUP BY post_id
)
SELECT posts.id <http://posts.id&gt; FROM posts_tags_cte JOIN posts ON
posts.id <http://posts.id&gt; = posts_tags_cte.post_id
WHERE posts_tags_cte.tags @> array[1, 2]::int8[]

But it gives me all the posts.

Aren't you looking for cte.tags = array[1,2]?

Hi Rob,

I figured it out. thanks. It is giving correct data.

Aren't you looking for cte.tags = array[1,2]?

posts_tags_cte has tags column, so I am using it.

Thanks,

Arup Rakshit
ar@zeit.io