-- Début de la recherche avancée dans le forum
SELECT
s.titre AS titre,
s.sous_titre AS sous_titre,
s.id AS id,
s.lu AS lu,
s.poste AS poste,
s.dernier_msg_pseudo AS dernier_msg_pseudo,
s.dernier_msg_date AS dernier_msg_date,
c.nom AS nom_cat,
c.id AS id_cat,
COUNT(m.id) AS nbr_reponses, -- VARIABLE DECLAREE ICI
s.annonce AS annonce,
s.ferme AS ferme,
COUNT(*) AS nbr_results
FROM
ns_sujets_forum s
LEFT JOIN
ns_messages_forum m
ON m.sujet = s.id
LEFT JOIN
ns_parties_forum c
ON s.forum = c.id
WHERE
(s.titre LIKE '%e%'
OR s.sous_titre LIKE '%e%'
OR s.contenu LIKE '%e%'
OR m.contenu LIKE '%e%')
AND nbr_reponses = 0 -- ET CA PIQUE UNE CRISE ICI


GROUP BY
c.id,
s.id
ORDER BY
c.id ASC,
s.annonce DESC,
s.dernier_msg_date DESC

Unknown column 'nbr_reponses' in 'where clause'

WHERE COUNT(m.id) = 0
-- Ou même
WHERE COUNT(m.id) = '0'

SELECT
s.titre,
s.sous_titre,
s.id,
s.lu,
s.poste,
s.dernier_msg_pseudo,
s.dernier_msg_date,
c.nom AS nom_cat,
c.id AS id_cat,
s.annonce,
s.ferme,
COUNT(*) AS nbr_results
FROM
ns_sujets_forum s
LEFT JOIN
ns_messages_forum m
ON m.sujet = s.id
LEFT JOIN
ns_parties_forum c
ON s.forum = c.id
WHERE
(s.titre LIKE '%e%'
OR s.sous_titre LIKE '%e%'
OR s.contenu LIKE '%e%'
OR m.contenu LIKE '%e%')
AND m.sujet IS NULL
GROUP BY c.id, s.id
ORDER BY c.id ASC, s.annonce DESC, s.dernier_msg_date DESC