Filter on two many to many relations - sql

Question

I'm trying to apply multiples filter on a table join to two tables
My tables
main
Id
Name
tags
Id
Name
main_primary_tags
mainId
tagId
main_secondary_tags
mainId
tagId
I want to select some items in main table which have some primary and secondary tags.
The difficulity is I need to have an exact result.
Exemple if I want to select items which have "Tag1 and "Tag2" tags, I want to have items which have both of these tags not just one of them (Like IN operator)
And I can filter on primary AND secondary..
Thanks for your help!

Answer 1

I would aggregate the tags into arrays and compare the arrays:
select main.id as main_id,
mt.tags as main_tags,
st.tags as secondary_tags
from main
left join lateral (
select array_agg(mpt.tag order by t.tag) as tags
from main_primary_tags mpt
join tags t1 on t1.id = mpt.tagid
where mpt.mainid = main.id
) mt on true
left join lateral (
select array_agg(mst.tag order by t.tag) as tags
from main_secondary_tags mst
join tags t2 on t2.id = mst.tagid
where mst.mainid = main.id
) st on true
where mt.tags = array['Tag1', 'Tag2']
and st.tags = array['Tag1', 'Tag2']
Note that the = operator for arrays depends on the order of the elements, so it's important to list them in the same way order by sorts them.

Answer 2

You can also do it like this
WITH tag_filter AS (
SELECT 'Tag1' AS primary_tag, 'Tag2' AS secondary_tag
UNION ALL
SELECT 'Tag1', 'Tag2'
)
SELECT m.*
FROM "main" m
INNER JOIN main_primary_tags mpt ON mpt.mainId = m.Id
INNER JOIN main_secondary_tags mst ON mst.mainId = m.Id
INNER JOIN tags primary_t ON primary_t.Id = mpt.tagId
INNER JOIN tags secondary_t ON secondary_t.Id = mst.tagId
INNER JOIN tag_filter tf
ON tf.primary_tag = primary_t."Name"
AND tf.secondary_tag = secondary_t."Name"
Or if you want something more compact in the tag_filter CTE
WITH tag_filter AS (
SELECT primary_tag, secondary_tag
FROM (VALUES ('Tag1', 'Tag2'), ('Tag1', 'Tag2')) t(primary_tag, secondary_tag)
)
SELECT m.*
FROM "main" m
INNER JOIN main_primary_tags mpt ON mpt.mainId = m.Id
INNER JOIN main_secondary_tags mst ON mst.mainId = m.Id
INNER JOIN tags primary_t ON primary_t.Id = mpt.tagId
INNER JOIN tags secondary_t ON secondary_t.Id = mst.tagId
INNER JOIN tag_filter tf
ON tf.primary_tag = primary_t."Name"
AND tf.secondary_tag = secondary_t."Name"
And in the case the tag_filter is much smaller than the main table, then you can also spool the tagId in the CTE, and then join with that instead.
WITH tag_name_filter AS (
SELECT primary_tag, secondary_tag
FROM (VALUES ('Tag1', 'Tag2'), ('Tag1', 'Tag2')) t(primary_tag, secondary_tag)
),
tag_filter AS (
SELECT primary_t.Id AS primary_tag_id, secondary_t.Id AS secondary_tag_id
FROM tag_name_filter tmf
INNER JOIN tags primary_t ON primary_t."Name" = tmf.primary_tag
INNER JOIN tags secondary_t ON secondary_t."Name" = tmf.secondary_tag
)
SELECT m.*
FROM "main" m
INNER JOIN main_primary_tags mpt ON mpt.mainId = m.Id
INNER JOIN main_secondary_tags mst ON mst.mainId = m.Id
INNER JOIN tag_filter tf
ON tf.primary_tag_id = mpt.tagId
AND tf.secondary_tag_id = mst.tagId