Why does it show 2 identical entries?

Question

PostgreSQL

Displays three entries, but two are the same

SELECT 
               :projection, 
               "user".firstname || ' ' || "user".lastname AS created_by,
               "campaign_status".name as status 
            FROM campaign
            LEFT JOIN :user "user" ON campaign.user_id="user".id
            LEFT JOIN :campaign_status "campaign_status" ON campaign.campaign_status_id="campaign_status".id
            LEFT JOIN user_group "user_group" ON "user".id = "user_group".user_id
            WHERE 
              "user_group".group_id = $groupId 
              AND (campaign.search @> '{"tags_in": [$tagId]}' AND not(campaign.search @> '{"contacts_out": [$contactId]}'))
              OR (campaign.search @> '{"contacts_in": [$contactId]}')
            GROUP BY campaign.id, "user".id, "campaign_status".id
            ORDER BY :sortBy :orderBy
            LIMIT $limit OFFSET ($page - 1) * $limit

Why might this happen?

Answer 1

I just passed a collection with tags and imploded it, then checked with IN().
As a result, the request turned out like this IN ('[10]','[20] и т.д.)and completely satisfied my task

Answer 2

Because it matches your data?
If it's not clear, simulate an elementary nested loop on your fingers, reading from your tables one at a time.