nton.sql

SELECT 
    p.*, 
    GROUP_CONCAT(t.tag_name) tagged 
FROM 
    tags_relation tr   
    INNER JOIN posts p ON p.post_id = tr.rel_post_id   
    INNER JOIN tags t ON t.tag_id = tr.rel_tag_id 
GROUP BY 
    p.post_id 

-- Other example

SELECT DATE_FORMAT(t.date, '%e/%m/%Y') as date, t.status, t.type, t.description, t.amount, o.name as other, GROUP_CONCAT(g.name) as tags FROM transactions t
        LEFT JOIN others o ON t.other_id = o.id
        LEFT JOIN transactions_tags tt ON t.id = tt.transaction_id
        LEFT JOIN tags g ON g.id = tt.tag_id
        WHERE t.account_id = ? GROUP BY t.id ORDER BY date DESC