Problème sql

CREATE TABLE sponsor
(
 idsponsor character(4) NOT NULL,
 idtypesponsor character(7) NOT NULL,
 CONSTRAINT pk_sponsor PRIMARY KEY (idsponsor),
 CONSTRAINT fk_sponsor_partenaire FOREIGN KEY (idsponsor) REFERENCES partenaire 
(idpartenaire) ,
CONSTRAINT fk_typesponsor FOREIGN KEY (idtypesponsor) REFERENCES typesponsor 
(idtypesponsor)
);
CREATE TABLE epreuve
(
 idepreuve character(3) NOT NULL,
 nom text,
 CONSTRAINT pk_epreuve PRIMARY KEY (idepreuve)
);
CREATE TABLE sponsoriser
(
 idepreuve character(3) NOT NULL,
 idsponsor character(4) NOT NULL,
 montant integer DEFAULT 0,
 CONSTRAINT pk_sponsoriser PRIMARY KEY (idepreuve,idsponsor),
 CONSTRAINT fk_sponsor FOREIGN KEY (idsponsor) REFERENCES sponsor (idsponsor),
 CONSTRAINT fk_sponsoriser_epreuve FOREIGN KEY (idepreuve) REFERENCES epreuve (idepreuve)
);

CREATE OR REPLACE FUNCTION distribsponsor(vidsponsor 
character(4), vmontant integer)
RETURNS VOID AS $$
DECLARE 
 vnbsponsor integer; -- nombre d'épreuves sponsorisées par ce sponsor
BEGIN
    -- nombre d'épreuves sponsorisées par ce sponsor
    select count(*) into vnbsponsor from sponsoriser 
    where idsponsor = vidsponsor;

    -- distribution du montant sur les épreuves déjà sponsorisées
    update sponsoriser set montant = montant + (vmontant/vnbsponsor) 
    where idsponsor = vidsponsor;
END ;
$$ LANGUAGE plpgsql;