Essayez ceci
SELECT i.*, o.organ_name, o.organ_logo, vtable.*
FROM heroku_056eb661631f253.op_ideas i
JOIN
(SELECT
COUNT(v.agree) as agree,
COUNT(v.disagree = 1 or null) as disagree,
COUNT(v.obstain = 1 or null) as abstain
FROM op_idea_vote v
GROUP BY v.idea_id
) AS vtable ON vtable.idea_id = i.idea_id
LEFT JOIN op_organs o ON i.post_type = o.organs_id
La réponse ci-dessous manquait le groupe par et la condition de jointure pour vtable