SELECT idCategoria, NombreCategoria, XMLQuery(
'for $x in collection("CatalogoCD")/catalogo/cd
let $artista := $x/artistas/artista[1]
return 
  <cd>
    <id>{$x/@id}</id>
    <artista> {$artista}</artista>
    <origen> {data($artista/@origen)}</origen>
  </cd>'
PASSING CatalogoCD RETURNING CONTENT
) AS AutorCDS
FROM Categorias