SELECT c.cod,c.denumire,(SELECT GROUP_CONCAT(cod_producator SEPARATOR '|') FROM mv_categorii_producatori cp WHERE cp.cod_categorie=c.cod ) AS producatori FROM mv_categorii c,mv_produse p WHERE FIND_IN_SET(c.cod,REPLACE(p.cod_categorie,'|',','))>0 AND p.=1 GROUP BY c.denumire --> query

Array
(
    [0] => 42000
    [1] => 1064
    [2] => You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '=1 GROUP BY c.denumire' at line 1
)
Array
(
    [0] => SELECT c.cod,c.denumire,(SELECT GROUP_CONCAT(cod_producator SEPARATOR '|')  FROM mv_categorii_producatori cp WHERE cp.cod_categorie=c.cod ) AS producatori FROM mv_categorii c,mv_produse p WHERE FIND_IN_SET(c.cod,REPLACE(p.cod_categorie,'|',','))>0 AND p.=1 GROUP BY c.denumire
)