including the result of one query in another query

Hi I have two databases, on for aeromodelistas (aeromodelling) and another for Códigos Postais (Postal Codes). I whant to do the following query SELECT CódigoPostal FROM Aeromodelistas WHERE CódigoPostal IN (SELECT distinct(CP4) FROM codigopostal.LOCART,codigopostal.DISTRITO WHERE codigopostal.LOCART.DD=codigopostal.DISTRITO.DD AND codigopostal.DISTRITO.DESIG='Coimbra'); This query is not working, and I do not know why. If I try the two queries individualy they work, togheter they don't!? But the question I want to put to the members of this list is the following. Is it possible to do the following? // first do the subquery $sql_CP4s = "select distinct(CP4) from codigopostal.LOCART,codigopostal.DISTRITO where codigopostal.LOCART.DD=codigopostal.DISTRITO.DD and codigopostal.DISTRITO.DESIG='$nomeDistrito'"; $resultado_CP4s = mysql_query($sql_CP4s,$ligacao); $linha_CP4s = mysql_fetch_assoc($resultado_CP4s); // then use it in the main query $sql_Aero_Dist_Masc = "select count(Nome) from Aeromodelistas where year(AnoQuota)=2005 and Sexo='Masculino' and Distrito IN $linha_CP4s"; How can we include the results (not just one) of one query in another query? Is it possible? Thanks. -- Pedro Henrique e Figueiredo Quaresma de Almeida