Error Code: 1271. Illegal mix of collations for operation 'concat'

[Oumar TOURE]

Bonour à tous,
Lors de l'exécution de ma requete ci-dessous j'ai le message d'erreur suivant; Error Code: 1271. Illegal mix of collations for operation 'concat'

select CONCAT(prefixe,annee,mois,jours,LPAD(IF(CONCAT(t.lastAnnee,'-',t.lastMois,'-',t.lastJours)<> dateCourante,0, t.numero + 1), 4, '0')) as nouveau_code
from (SELECT
code,
MID(code, 1, 1) AS prefixe,
MID(code, 2, 4) AS lastAnnee,
MID(code, 6, 2) AS lastMois,
MID(code, 8, 2) AS lastJours,
MID(CURRENT_TIMESTAMP, 1, 4) AS annee,
MID(CURRENT_TIMESTAMP, 6, 2) AS mois,
MID(CURRENT_TIMESTAMP, 9, 2) AS jours,
MID(code, 10, 4) AS numero,
CURRENT_DATE as dateCourante
FROM demandeur
ORDER BY code DESC
LIMIT 1
) as t

Merci de m'aider.