Prueba esto:
Código SQL:
Ver originalSELECT *
FROM
(
SELECT conceptos.codigo,relacion.posicion
FROM conceptos,relacion
WHERE conceptos.id = 7
AND relacion.id_padre = 11
AND relacion.id_hijo = conceptos.id
UNION ALL
SELECT conceptos.codigo,relacion.posicion
FROM conceptos,relacion
WHERE relacion.id_padre = 7
AND conceptos.id = relacion.id_hijo
) AS t
ORDER BY 2;